Rule no. 1: don't blame healers
Healing isn't always fun. It takes a certain kind of player to roll a heal-enabled class and actually heal. This is why players should turn off that annoying AddOn emote. Most healers know what they're doing. If they're in the Battleground with you and they're specced to heal, chances are they heal instances and raids, too. This means that all they do is heal. Even though I used to re-spec about five times a week while we raided, I almost never spec to specifically heal if I'm wanted to do Battlegrounds (Arenas, needless to say, are another matter altogether). But if you're grouped with a healer in a PUG, it's a good bet that they heal all the time... so cut them some slack.
Good healers won't be reading the chat log to see who needs healing. They might have Shift-V toggled to see who needs help, watch party unit frames, or use AddOns like Healbot Continued. Healers normally have means of finding out who needs healing, so you really don't need to remind them. Furthermore, players should simply not expect healing in a PUG -- it's good when it comes, but it shouldn't be something you depend on. If you fall in battle, it's nobody's fault but yours (and, well, the four other people trying to smash your face in). Once you take that attitude into the Battlegrounds, you'll worry less about getting heals and focus more on getting your opponents down quicker.
Rule no. 2: protect your healers
Just as healers work hard to keep you alive, do them a favor by watching out for them. If you see an opponent target a healer teammate, throw yourselves in harm's way. Crowd control is a good means of slowing down an opponent's attack on an ally. It's often not a good idea to try and outdamage the attacker in the hopes of killing him before he kills your healer, because unless it's a tanking Discipline Priest or a IWIN class Druid, there's a fair chance they'll kill the healer first. Always have Show Target of Target toggled in your Interface options. This allows you to see if your opponents are looking the wrong way at your healers. If you're engaged with another target, it will sometimes help to switch targets in order to buy your healer some time. If you have a dispel or protective ability, throw it your healer's way.
Rule no. 3: neutralize their healers
I don't think it can be said enough times -- unless you have massive DPS, say, like all ten of your teammates focus firing on one target, kill the healers first. Unless you have some sort of Mortal Strike or Aimed Shot debuff on the target, an opponent backed by good healing will be impossible to kill, so don't even try. This is why heal reducing abilities are so key to PvP, particularly in Arenas where MS Warriors have cemented their place as quite possibly the most popular class. A Rogue can use Wound Poison, which can be applied very quickly and stacks. Unfortunately, it's also removed by abilities such as a Druid's Abolish Poison; a Shaman's Poison Cleansing Totem or Cure Poison; or a Paladin's Cleanse. Mortal Strike or Aimed Shot are both Physical debuffs, which are harder to remove.
Use crowd control freely and often, specially against healers, who are often the ones with the ability to remove them with Dispel Magic or Cleanse. A sheeped Priest won't be able to un-sheep. A feared Paladin won't be able to un-Fear except, of course, when they bubble -- which is why you fear them anyway, so they use up their trump card early. If a healer can't be killed, crowd control them long enough to kill their allies. One of the biggest mistakes in games like Warsong Gulch is focusing on the flag carrier without neutralizing their support. While sometimes there's enough firepower to overcome healing, it certainly makes the job easier when you put the healer out of the picture. Here are a few tips when dealing with enemy healers:
Druids are the most difficult class to catch. Aside from their superior mobility, they are immune to Polymorph, too. Because of their stacking Heal-over-Time spells, it is important to find means to remove them with abilities such as Purge or Dispel Magic. With enough HoTs, a Druid can regenerate more health than most DPS can dish out, making them or their allies a real pain to deal with. The best way to neutralize druids is to probably to crowd control them, as they'll probably last longer than the DPS they're trying to protect. Fear and similar effects work very well as they have no natural counters against them. It is important to note that Druid forms are also susceptible to different kinds of CC: Cat Form, Travel Form, Bear/Dire Bear Form, and even Flight and Aquatic Form are all categorized as beasts, allowing the Druid to be put to sleep or feared. Tree of Life is considered an elemental, so Warlocks can Banish them, although it'd probably be funny if they took more damage from fire spells, too. Moonkin Form is humanoid, so restrictive abilities like Sap and Repentance work. The important thing is to be prepared to react to whatever form the Druid takes, specially if they lapse into their default racial form. This is when they are most vulnerable, particularly to physical damage.
Bait their bubble early. This is key to controlling a Paladin healer. Put them on the defensive by dealing massive amounts of damage or subjecting them to chain crowd control, which should force the Paladin to use Divine Shield. If you're a Priest, needless to say, Mass Dispel will make short work of their immunity. Otherwise, wait out the 12 seconds and return to the Paladin, who will now have Forbearance, preventing the use of similar immunity effects or even Avenging Wrath. This is when a Paladin is most vulnerable, so take advantage and try to take them down within that one minute window. Paladins also have no HoTs or instant cast heals aside from the soon-to-be-buffed Holy talent Holy Shock, so they need to stay still in order to heal making them very vulnerable to attacks or spell interruptions. As flag support in WSG or Eye of the Storm, Paladins must stop to heal so it's easy to separate them from their targets causing them to go out of range. Unlike Druids, who enjoy movement fluidity, Paladins can be locked down rather easily the moment they stop to heal.
A Discipline Priest is quite possibly the most difficult class to take down under most circumstances. Armed with powerful shields and buffs, as well as Renew or Prayer of Mending, sometimes the best offense against a Priest is a spam of Purges. A Weakened Soul debuff will prevent the Priest from being shielded again very, very briefly, allowing a small window for damage to penetrate. Time your highest damage spells or attacks when the Priest has her shield down. Priests will almost always have a shield up, making it very difficult for damage to get through (and gives Warriors 0 Rage). Priests can also resist fears and stuns very well, adding to their resilience. One thing that Priests are susceptible to, however, are Poisons and Curses. Viper Sting, Wound Poison, Mind-Numbing Poison, and Curse of Tongues are all good abilities to use against a Priest if not necessarily to kill them but to slow down their healing long enough to have your damage make a difference.
Shaman healers are also HoT-less wonders, requiring them to stop to heal every time. Aside from the bonus that Nature's Swiftness confers, Shamans need to stop to heal, similar to Paladins. They have Earth Shield to help with this, so this needs to be Purged or dispelled. More than other healing classes, Shamans are excellent offensive support, often having Windfury Totem down, for example, when grouped with Rogues or Warriors. While these won't keep the Shaman alive longer, it'll certainly make your life shorter as her allies bear down on you. Kill the totems. Most totems have only 5 life, so have a macro prepared to target and destroy them. You can also set the Shaman as your focus, enabling you to quickly return to your target after deviating for totems. By neutralizing totems, you eliminate an important part of the Shaman's arsenal. If they try to escape as a Ghost Wolf, remember that the spell classifies them as beasts, so they can be put to sleep or feared.
Rule no. 4: thank your healers
Unlike DPS classes, there's little glory to be had with healing. The default hierarchy listing in a Battleground is through Honorable Kills, which favors the DPS classes. Sure, healers can enlarge their epeen, too, by toggling the Healing Done hierarchy, but it gives you more of a tingly feeling inside rather than strike fear into the hearts of enemies. There should probably be a 'Butts Saved' category right beside Honorable Kills, but healers will have to compete with the seems-to-proc-way-too-often Cheat Death. Thank them. Shower them with praise. Look at your combat log and see who saved you from that 4k Shadow Bolt. Healers like that. I guarantee you that if you praise them by name on /bg chat, you'll get a little more attention. Healing is usually a thankless job, so every little bit of encouragement helps. Even if you forget to thank them, don't forget rule no. 1.
Rule no. 5: roll a healer
Perhaps the best way to understand how healing in PvP works is to actually roll one. Unlike most dungeons or raid encounters, PvP requires the healer to move. A lot. This is an essential paradigm shift from raid healing. At the same time, unless it's an Arena tournament, there's much less pressure to heal. If someone dies, well, there's always the Spirit Healer to throw him back into the fray. PvP healing is incredibly dynamic, and can vary from incredibly easy (e.g. a Rogue poking his little toothpicks into a burly bear Druid) to the hopelessly difficult (e.g. a Mage with Mortal Strike applied while a Warrior, Rogue, and maybe a Warlock casting Soulfire for good measure are trying to crack him open like a piñata).
There can never be enough healers in PvP -- well, except perhaps for that one Warsong Gulch match where there were eight of us healers and a somewhat undergeared Rogue and Hunter. That painful memory is more the exception than the rule, however; everyone welcomes another healer in the fighting ranks. If you've never played a healer before, it might be jarring at first because you'll be making more use of the mouse to point than to move. If you heal, use an AddOn like healbot or, if you're a minimalist, the all-important mouseover macro, which looks something like this:
/cast [target=mouseover,exists] Flash of Light; [help] Flash of Light; Flash of Light
Simply replace Flash of Light with the appropriate buffing or healing spell. This handy little macro will allow you to heal any unit frame -- from their character portrait in your party list, to the raid window you've dragged out, to the name plate above their head, to their life bar, or even their avatar itself. If you mouseover a valid target, the spell will go off. Otherwise, your mouse pointer gauntlet will glow blue, allowing you to select a proper target. Mouseover healing will also allow you to keep your current target without deselecting it, so you can keep your focus on enemies while healing at the same time. If you have Show Target of Target toggled (and you should), you can even heal the unit frame that your target has selected. Sound confusing? It's not, really. Healing in PvP is a challenging role that can also be very rewarding. As long as people remember the healing rules, that is.
Zach Yonzon writes the weekly PvP column The Art of War(craft) whenever he isn't CC'd by his nearly four month-old daughter.