My guild runs with, in my opinion, a nice set of tanks. I can’t think of any times recently where we’ve wiped on a boss because of tank*fail, and I never sit there and want to cuss my tanks out for sucking. That said, they have shown me, through good example and maybe otherwise, that there are small things that healers and tanks can do for each other that can make raiding a lot smoother, practically speaking and socially. LET ME SHARE THIS WISDOM.
I won’t address the more obvious, terrible things in this post because as I said, I raid with competent tanks. If you’re pugging, or have crappy tanks, you might be struggling with bigger issues, but these are the small things — the smile points, if you will.
Mana: No healer loves a tank that pulls trash when they’re oom, and no tank likes waiting for a healer to sit there and get their mana to 100%. The compromise? Healers, don’t FREAK OUT when your tank chain pulls trash and you’re at 60%. Sit down to drink the instant you’re out of combat, pop a mana pot if you’re really chainpulling hard, blow your mana cooldowns if you’re far enough from a boss pull, or just plain deal with not being topped off all the time. You heal through bosses that are much more intensive and longer than any trash, deal! Tanks, don’t pull another pack if your healers are obviously dealing with a lot. Don’t run ahead and get angry when your healers are sitting back a few seconds to drink (though the flexible healer will run up with you unless they’re really low). Give your healers time to rez the morons who stood in Hurricane
Pulling: I can only speak about this from a disc priest perspective in particular, but I’m sure other healers have their own spells or buffs or whatever they can substitute. One of the nicest things a tank can do for me is ask for a shield before they pull. Like it’s part of their ready check — “Can I get a shout and a shield…pulling!” I think recognizing who’s healing you and what they’re doing is a really good way to make a healer feel important and let them know the tank knows a little bit about their healer’s job. It’s not necessarily an ego boosting thing, but it’s just nice. Healers can help foster this by being consistent, attentive to when the tank is ready, and being communicative about cooldowns, buffs, etc. It can be very frustrating to have a tank who aggros just before I can get a shield and PoM off, and I get nasty trash aggro >.<
Messing up: During the few years I’ve been playing, I’ve seen a lot of blame get thrown around during wipes. My current guild doesn’t usually get nasty, but everyone runs into finger-pointing sometimes, even if it’s through more private channels. A dangerous trap to fall into is *the healers are always the reason we die*. Of course, this is true sometimes, and bad healers on some fights can mean death more quickly or assuredly than bad dps (Mimiron, XT, sometimes Hodir). But there is nothing more gratifying than someone stepping up and actually taking some of the heat, especially to help out the healers, and especially if it’s a tank. “That was totally my bad, I was tanking him way out of range,” “I didn’t move out of that void zone,” “I blew my cooldown too early,” etc, are amazing words to hear from tanks, instead of “Uhh I guess I didn’t get any heals,” or “You need to keep me up better than that.” Healers, same goes for us. You fucked up? You don’t think you can handle a certain assignment? Say something. Did the tank obviously fuck up? You don’t need to point it out, but done tactfully, defending your own and others’ healing can at the very least help tanks from getting huge epeens or martyr complexes!
((Also: the less you bring up your bad lag or framerate, the less annoying you’ll be, even if it’s your legitimate excuse. I have a terrible computer, but only rarely do I say, “hey guys, I don’t know if I can handle the timing for this, I don’t really trust my computer,” and I almost NEVER blame my mistakes on lag retroactively. “My fault, sorry” is usually enough, unless probed. Don’t make them doubt your consistency by bringing up your system problems.))
Being super serious: It seems like, in general, tanks and healers have to be more serious than dps. I don’t quite know why, but in a lot of the guilds I’ve been in, the dps seem to be at more leisure to joke around and relax than many of the tanks and healers. Some unspoken rule of importance of role or something, I suppose. My suggestion? We can all lighten up some, without becoming baddies. Maybe just a /highfive to your awesome tank when you solo heal him during IC, a random joke demonstrating comaraderie when your pet healer runs behind you to pull the next pack. My guild is great about this — silly stuff that doesn’t affect your game by distracting you, but helps strengthen what is really the most important set of in-combat relationships in the game. Don’t you want a healer to LIKE healing a tank?

I need a witty picture of me and a tank, don't I
\jj/
-Kivuli