Before you say Pah! I don't need to do anything to keep my healer happy -- I massively outgear all the 5-man content the game has to offer. This advice is worthless!, spare a thought for those who don't. The new healer who wants to get a look at some Hour of Twilight. The player with bags overflowing with PvP gear to cheat the ilevel requirement. The fresh 85s who are facing these dungeons for the first time. They need this advice, and if you're running with them, you could consider reading it too. And if you think it's not your responsibility to help your healer out now and then, remember: You don't do any DPS when you're dead.
- Don't stand in bad. I can't emphasize this enough. If you suddenly see big, angry damage taken numbers coming up on your screen, you are standing in bad. Move. Some bad is more bad than other bad; examples of very bad bad to stand in include the purple rivers periodically chucked out by Echo of Sylvanas' Blighted Arrow in End Time. There is no unavoidable ability that kills you in a matter of a few seconds, so if you're dying that fast, there's something you should be doing about it. And even if you are moving out of bad, you could probably move faster. There's usually a moment before the bad stuff starts dissolving you from the feet up, so get out of there before that happens. And if the tank moved so that he wasn't in bad but the boss's back end still is? Just move out of the bad. Your DPS may drop a bit from not attacking him from the perfect angle, but it won't drop as much as it will if you're dead.
- Pay attention to the mechanics of fights. Zul'Gurub is a great one for this. The group gets to Zanzil and decides to use the patented red cauldron method where everyone takes the red cauldron buff and DPSes the boss from melee range. Great, if it works. Not great if you're a low-geared healer and your group includes a warlock and a mage. Even less great if the DPS aren't as DPS-y as they think they are and Zanzil casts Graveyard Gas but nobody notices in time. Or if the lone berserker ambling around kills your healer who's trying to save your backsides with something that requires a cast time. And I know Archbishop Benedictus' obvious wave of obviousness "isn't a one-shot," as one tank eruditely pointed out, but is it going to mean the fight takes twice as long if you avoid it? No. This is linked to point #1. If you're planning to red cauldron it up or to not avoid the wave, check with your healer before doing so. If they say don't, then don't.
- Watch your aggro. You heard me -- you, the mage over there doing the crazy numbers. Let the tank establish an aggro lead -- it only takes a couple of seconds -- then attack what he's attacking. The tank is designed to take huge hits to the face; the mage is not. And yes, the tank can taunt it back -- that would be lovely -- but once the mob starts retreating back toward the tank, that's not the time to unleash your mightiest DPS cooldown. Your armor is basically very pretty origami. Omen is your friend here. Healers can also chuck out quite a lot of aggro, but usually it's because they're rolling out the big guns trying to prevent a wipe. Bear that in mind, and remember that if your healer dies because something is eating their face, you probably will too. On the same topic, try not to be That Guy who always stands where another patrol will be or just in aggro range of another pack. Pay attention to your surroundings, not just to your meters. Oh, and DPSers, let the tank pull. If you're stressing because they're going too slowly, feel free to leave and head back into the 35-minute queue.
- Interrupt things. All classes have the ability to do this somehow, albeit with varying provisos, ranges and cooldowns. An awful lot of very, very tiresome abilities are interruptible, including ones that do a good amount of damage. Many mobs will keep chain casting those abilities until interrupted, such as Arcurion's Hand of Frost, so just interrupt it. Please. The less damage the group takes, the less mana your healer gets through, the fewer breaks you have to take, and the faster you'll progress through the instance. And the less likely it is that you'll wipe.
- Use your abilities. But I am! I hear you cry. I'm spamming these damage abilities like it's going out of fashion! Of course you are, but are you using those other ones? The stuns? The ones that remove enrages? Have you made your healer a Mana Cake recently? Have you noticed your health getting low and used a heal on yourself? Have you dispelled a curse or used Dark Simulacrum or Spellsteal to, well, steal a spell? Are you using crowd control? Are you putting debuffs on the boss? Are you occasionally using a defensive cooldown if your health is low? Are you popping out a Tranquility when things are going pear-shaped? If you're doing all these things, then thank you. You're making your healer happy.
And if your healer gets angry with you for using your abilities, healing yourself, paying attention to the mechanics and the like, then don't worry. You're doing the right thing -- and while you may have angered one of the 10 million or so people who play WoW, you'll make many others very much more cheerful.