In World of Warcraft, player verses player (PvP) can be  defined in many complicated layers.  In  the simplest terms it just means killing the other player, but in the realms of  Azeroth, the venues where it occurs can mean that PvPing often involves a lot  more than just mowing down a lot of enemies.
You should know that venturing into battlegrounds the first  time is super intimidating if you have no PvP experience.  You can negate this by reading some strategy  guides and replacing your nervousness with confusion.  Or, you can just go in, copy other players  until you kinda figure it out, and have a good time doing it.
But if you do want a guide, there are hundreds out there on  how to PvP in WoW: how to kill the other guy as swiftly as possible, how to  maximise your class abilities, how to win battlegrounds the most efficiently,  overviews of PvP etiquette, and discussions of strategy.  This is not one of those guides.  Or maybe this is all of those guides.  Mostly this is my own guide: one part fun,  one part silly, one part useful.
Basic Tips For Everyone
•  PvP is not always  about killing your enemy.  It is also  about crowd controlling, stunning, incapacitating, distracting, kiting and  disorienting them.  Be smart and know  when it’s better to stun someone and move on to something more important rather  than always staying for the killing blow.
•  Communicating in  /bg is paramount.  Call out when enemies  are about to attack an objective (resource node or flag), where the flag  carrier is headed or hiding, or where you are heading with the flag.  Be brief and clear; avoid chatspeak but do familiarise  yourself with battleground-relevant acronyms.
•  Become familiar  with your “get Away” abilities, like Blink, Sprint, Vanish, Disengage,  Earthbind, etc.  Always have a plan of  action for escaping a fight you know you will lose.  Some of these abilities will clear debuffs or  movement impairing effects and others you will need to pair with another  ability.
•  Kill healers  first.  Kill healers first.  Kill healers first.  If you can’t do that: crowd control, stun,  fear, incapacitate, interrupt, knockback, relocate or distract the healer and  keep them away from their target.  By the  way, kill the healer first.  They should  always be your primary focus target as long as they are nearby.
•  Know when to use  your keyboard and when to use your mouse.   The usefulness of keybinds in PvP can’t be emphasised enough.  PvP is largely about quick thinking and fast  reaction times, and keybinds are pretty much the only way to do this.  On the same token, get used to mouse movement  because keyboard turners are at a huge disadvantage.  You can also do things with your mouse like  jump while running, turn around and instant-cast something, land facing forward  and keep running without missing a beat.
•  In PvP, instants  are awesome because battlegrounds are often high movement and you don’t have  time to stop long enough to cast a big nuke or giant heal.  Next best is things with a quick cast  time.  Not only do they make it so you  don’t need to be a sitting duck for as long, but they a lot harder to catch  with an interrupt or silence.
•  Heals, dispels and  cleanses are a big deal in battlegrounds.   They can often make or break a game.   If you really love DPS and hate playing as support, then go ahead and  stick to that, but a truly good PvPer will know when to use any heals or dispel  in their arsenal, either on yourself or on your teammates.  It is often better to heal, even in DPS gear  and spec, if there are no other healers around to help your teammates, or if  you think it might be more advantageous to just heal yourself while you wait  for reinforcements to arrive.
•  One really  important thing in pvp is to know when to walk away and how to pick your  fights.  Your teammates (and your  enemies) will often be prone to stopping to fight anyone they see, even if  killing that person won’t aid the objectives or there is no way they will be  able to kill that person in a timely fashion.   Don’t get in heated one-on-one battles while your team is off doing  something else, don’t stop to fight people in the middle of the map for no  reason, and don’t engage in a fight you know you can’t win unless there is some  legitimate strategy to it (ie, distracting the enemy).  If you avoid this, you’ll not only be a  better player but you’ll also find yourself actually winning more games.
•  Using PvP gear in  PvP makes a larger difference than a newcomer might expect.  Health and resilience impact your survival  just as much as smart gameplay.  If you  have nothing else, fly over to Wintergrasp and buy the heirloom PvP trinket  until you play enough games to buy youself a whole set.  Even if you have a really good PvE piece, it  is often still better to use a lower quality PvP piece in that slot.
•  Learn how to use  terrain, range and line of sight to increase your survivability.  This takes practice and a different mindset  than you may have from PvE, but it will help you a lot if you master it.
•  Nameplates are very  useful in battlegrounds, both for watching your teammate’s health and for  monitoring enemies.  It will let you know  which guys are close to dead and also make it easier to target them and see  them coming.
Learn Your Class Again, Because Everything You Know Is Wrong
Before you ever enter a battleground, the first thing to  know is that many of the spells you like in your dungeons and raids are stupid  and lame in battlegrounds.  That rotation  you’ve got down perfect is useless.  And  those weird abilities you got and never even put on your bar because “when the  hell will I ever use that?” may end up being your favourite spells.
Look through your spellbook and consider something’s  application against another player and the spells they may be using.  If you’re not sure if something is good or  not, ask yourself: how much will this piss of the guy I use it on? If the answer is somewhere in the realm of “a  lot,” then it is probably an awesome PvP ability.  Here is the secret to fun PvP: it’s not about  killing the other guy, it’s about frustrating him endlessly.  Sometimes that involves killing him, but it  also can involve things like a well-timed sheep.
At the risk of becoming a class guide, here are some spells  each class should learn to love:
Mage:
•  Sheep people often.  The best times to do this are: when they are  casting their big nuke spell, when they are about to heal someone, when they  are running a flag or guarding a node, or just because they’re the only person  around and you have the mana.  You don’t  even need to fight them afterwards; if they’re just some random guy on the  road, it’s better to sheep him and then run off to do something more  important.  Protip: you can sheep people  off their mounts.
•  Counterspell casters on cooldown.  Especially healers.  Nothing is more satisfying than that  beautiful noise signifying that someone is probably going to die soon.
•  Frost Nova melee in places where they  will be useless.  Actually, if it’s off  of cooldown, go ahead and frost nova them no matter where they are.
•  Frostbolt and Cone of Cold are both awesome, even if you’re a fire mage.  Why?   Because it slows people, and slow people are almost as useless as dead  people in battlegrounds.
•  Blastwave, if you have it, is  good for relocating your enemies and interrupting their abilities.
•  Iceblock not just makes you immune to  incoming damage but it will clear your debuffs so you can get back in the game.
Warlock:
•  Fear is your new favourite  ability.  Your should use it as often as  possible, and at the times when it will anger your opponent the most.
•  Put Curse of Tongues on all the  casters.  Even if they can remove it,  that’s still one more GCD when they’re not casting that heal or fireball.
•  Fall in love with  your Succubus and Felhound.  Your succubus can seduce people, like healers  who are healin’ a bit more than you’d like or that really buff warrior who is  beating on you, and your demon puppy can spell lock anyone who you’d prefer not  be able to cast.
•  DoT everyone (okay, that’s not one  ability).  Seriously, put your debuffs  and Damage-over-Time spells on anything that moves.  Just tab around and make sure everyone is  feelin’ the hurt.  You have a good chance  of killing people this way, and at the very least, the healer is going to be  spending a lot of time dispelling his teammates instead of casting heals.
•  Use your Drains.   Lifedrain and manadrain benefit you at your enemy’s detriment.  Awesome.
Priest:
•  Psychic Scream every time you can.  It’s best used by running into a crowd of  people before dropping it, but go ahead and use it on that one guy beating on  you, too.
•  Mana Burn is great on healers,  especially ones that are already low from slamming big ones on their teammates.
•  Silence, if you have it.  Of course.
•  Bubble your teammates that are getting  beat on.  It doesn’t matter if you’re a  healer; the rogue beating on your buddy will hate you for it, and that’s what  counts.
•  Mass Dispell not only will remove magic  debuffs from your teammates but also buffs from your enemies.  Best of all, it removes things like a  paladin’s invulnerability bubble: the only thing in the game that will.  Use it on large groups of people fighting and  also on paladin bubbles.
•  Mind Flay slows people, and because  it’s channeled, will automatically turn you to help you follow runners.  Also it damages people, which never hurts.
Rogue:
•  Stock plenty of Crippling Poison, Wound Poison, and Mind-Numbing  Poison.  Ideally, you want to have  spare weapons to swap around for each in the appropriate situation.  Slowing player movement, delaying their  casts, and making their heals weak are both extremely useful and very  enjoyable.
•  Stuns are the thing you’re most loathed  for.  Stun as often as you can.  Open with cheapshot and use kidney shot as  your finisher.  If necessary, vanish so  you can cheapshot a second time.
•  Cloak of Shadows will surely piss off  that warlock who just spent a bunch of time DoTing you up.  Bonus points if you use it when he has like  .2 seconds left on his big nuke, so that way he still wastes the time and mana.
•  Sap any people you cross out of combat,  whether they are defending something or just merrily prancing around.
•  Dismantle will disarm your melee foes  and Blind will disorient them.
Druid:
•  Shapeshift can be used to your  advantage in a lot of ways.  Use it  liberally to break snares.  Also know  when is the right time to be in the right form; sometimes it’s better for a  moonkin to bear up and wait for help than to try to fight it out.  Lastly, remember, you’re immune to polymorph  when in form.
•  Hibernate works on hunter pets, shaman  in ghost wolf, and other druids in cat, bear and cheetah form.  Don’t be shy about using it.  The awesome factor goes up if you use it on a  wolf or cat running a flag.
•  Cyclone not only crowd controls your  opponent, but it won’t be broken by your teammates incidental AoE, and the guy  stuck in it won’t be healed from it.   When one guy is immune, just use it on another.
•  Typhoon, if you have the ability, is  great for knocking around enemies (including off of nearby cliffs) and  interrupting their spellcasts.
•  Use Roots on anything that’s going  somewhere you don’t want it to.
Hunter:
•  Wing Clip is a good way to slow down  your opponents, whether they’re running the flag or chasing down your healer,  or just because you need to get range.   In all circumstances, it will annoy them, which alone makes it valuable.
•  Know your Shots, because depending on your spec,  you can use different ones to silence, slow, sleep, and disorient.
•  Traps are awesome and you should make  heavy use of both freezing and frost trap, depending on the context.
•  Disengage is a very handy way to get  away from a melee attacking you, to get range on someone, or even to bounce out  of someone’s cast range.
Shaman:
•  No matter your  spec, Frost Shock is great for  slowing people.  Pair it with an Earthbind totem and you can do fairly  decent kiting of melee.
•  Grounding Totem is your best friend  against casters.  Drop it on cooldown  anytime one is nearby.  And don’t forget Tremor Totem to break pesky fears.
•  Purge removes buffs from your  enemies.  This works on more than just  things like Intellect and Fortitude: it will also remove things like speed  boosts and heal-over-time spells.   Happiness is purging the HoTs off a tree.
•  Thunderstorm is a great knockback if  you have it.  It is good as both an  interrupt and a fun way to abuse your enemies.   Shaman are especially fond of using it to toss people off of cliffs when  they get to close to the edge.
•  Wind Shear is your bread-and-butter  interrupt, and it’s off the GCD.  It’s on  a very short cooldown, so use it on those casters over and over and over  again.  Picking a healer and waiting  until their big heals are about finished to cast is both practical and  extremely delightful.  Or, pair it with  purge to destroy an oft-invulnerable restoration druid.
•  Hex is on a long cooldown, but it’s  still great to use to crowd control people, interrupt their casting and make  them an adorable frog.
Paladin:
•  Your Self Bubble is the thing everyone  loathes you for.  Use it regularly to  grant yourself immunity when running away or healing yourself to full.  Remember it will make your drop the flag if you’re carrying it.
•  If it says “Hand of” on the title, it’s probably  great for PvP.  Freedom will break slows  and snares and should be used liberally on yourself and your teammates.  Hand of Protection is splendid to use on your  spellcasting and healing teammates to protect them from melee attacks (just  don’t use it on physical DPS).  Sacrifice  can be used to overcome abilities like sheep which will break on damage.
•  Hammer of Justice is on a longish  cooldown, but it’s a great stun so don’t be shy about smacking people with  it.  It comes with a highly satisfying  BLAM! noise to remind you of how great it is.
•  Repentance is Retibution’s crowd  control and can be used in combat.  Use  it on that healer in the back or the guy playing defense.
•  Judgment of Justice will prevent your  opponents from moving any faster than runspeed, whether they’re mounted or in  travel form, or popping sprint.
Warrior:
•  Berserker Rage is a great ability that  breaks fears and incapacitates and should be used off of cooldown.  Use it in conjunction with your trinket and  you’ll find these abilities effecting you half as often as anyone else.
•  Hamstring will slow your opponents and  can be used on as many people or as many times as you have rage for.  If you can, tab around and hamstring anyone  who is melee DPS.
•  Disarm will cripple any melee  opponent.  It’s on a decent cooldown, but  don’t forget to use it when a rogue is beating on your healer or you’re locked  into combat with a Death Knight.
•  Stuns should be used liberally if you  have them.  All warriors have Charge, but  if you’re Protection, you’ll also have Shockwave and Concussion Blow, which are  both very powerful.
•  Pummel is great for interrupting  spellcasting; every warrior should be prepared to Stance Dance to use it, or  toss on a shield quickly for Shield Bash. 
•  Few things will  bring you as much joy as Spell Reflect,  especially when you use it on a shaman about to Hex you or a mage coming at you  with pyroblast.  You should carry a  shield for this ability alone.
Death Knight:
•  Deathgrip has a lot of utility in PvP,  on top of being very fun to use.  You can  suck in players to interrupt their spellcasting, prevent them from hurting a  teammate or capturing an objective, or getting them into range for you to kill  them.  Use it with a smile and use it  often.
•  Strangle is your silence to deal with  those pesky casters.
•  Use Chains of Ice to slow opponents running  away from you or towards a friendly.   It’s also fun just to toss on random people who are running by.  They want to be somewhere else, so appreciate  how fun it is to deny them that.
•  If you’re Unholy,  your Ghoul provides interrupts and  stuns, so stick it on a caster target while you beat on someone else.
Approaches to Battleground
Although killin’ your foes is always superduper, what’s most  important for success is different in every battleground.
Warsong Gulch
Warsong Gulch is a game of capture the flag.  The most important things that you can do in  this battleground is protect your team’s flag carrier – by healing him or  killing the people attacking him – or by returning our flag from the enemy – by  killing him, or healing your teammates who are.   In this battleground, slowing or stopping the enemies is almost as  valuable as killing then, moreso if you can slow multiple people.  Don’t get distracted fighting people  mid-field.  Lastly, play to Offense if  you can as you really only need a person or two on Defense in this game.
Arathi Basin
Arathi Basin is about earning more resources than your  enemy.  You do this by capping and  holding three resource nodes and defending them.  Playing defense is just as important as  taking nodes.  Always watch on your zone  map to make sure every node you own is adequately protected.  Offense may be more fun, but if no one is  guarding, be the responsible player who does, or it could mean the game.  Final tip: never fight on the road, always  near a flag.  Not only will you spawn  closer to your graveyard, but you will be able to keep an eye on the flag at  all times.  Roadfights are very common  but don’t get sucked in.  You can,  however, use them to your advantage if the enemy team is not watching their  flag, allowing you to sneak in from behind and cap it.
Strand of the Ancients
In the Strand, the goal is to get the relic at the end of  the battlegrounds, and to prevent your opponents from doing the same.  On offense, you need to use demolishers to  break through a series of gates.  It is  best to let melee players drive and use ranged, crowd controllers and healers  as passengers to help defeat the enemies attacking your vehicle.  In defense, your top priority is always  killing demolishers, either directly or by healing your DPS teammates.  Do not get distracted by players running  around: always go for the demos.
Isle of Conquest and Alterac Valley
Both battlegrounds are different maps for the same  objectives.  The goal is to either defeat  the enemy’s general in their keep, or by depleting their reinforcements.  Capturing and holding the various objectives  on the map will help your team and also grant you honour points.  Always try to find near and for these  objectives rather than get caught in some random fight off on the road.