1) If you are overgeared for a certain instance - which a ton of people are (I don't think I've seen a healer that isn't overgeared for dungeons like roic Nexus or UK) - pick yourself up a Darkmoon Card: Twisting Nether. Basically, it acts as a free soulstone 10% of the time. If anyone messes up, probably an additional small amount of spellpower/mana probably won't save you. If it will, then by all means keep your snowflakes or pictures equipped; however, usually, it's an issue of threat or the tank picking up the wrong adds, and it's a 1-hit KO either way.
However, if you have the slightest doubt about your performance in a heroic, have everything (including your best gear) ready! Flasks, potions, reagents, food, the works (keeping a few feasts around always makes group members happy). Also, don't have this equipped in the new heroics. You'll need to be on your toes every moment.
2) Fear, though not as present as in BC, is still a factor in the equation. There are 2 spots I notice it most frequently - the trash pulls in the end of DTK, and some random guys in UP [edit: also, Halls of Reflection trash. But it can get so messy there, it's not really a specific mechanic that needs worrying about]. Probably exist other places as well, but it doesn't spring to the top of my head as I think about it, so it's probably not all that annoying.
However, you can be SURE that the last two pulls of DTK will always be aggroed together, because of fear, and you can also be sure that King Dred will make your life miserable with his own roar of fear-inducingness. A wonderful counter to this is equipping a PvP Trinket (or using the racial if you're human) - or just spamming hots. Effective management of fears can mean the difference between a wipe and a clean kill, and if you're really unlucky - it doesn't matter HOW geared you are.
3) Here, there is a very fitting quote from Simon Tam, medic of Firefly:
Simon: No matter what you do, or say or plot, no matter how you come down on us… I will never, ever harm you. You're on this table, you're safe. 'Cause I'm your medic, and however little we may like or trust each other, we're on the same crew. Got the same troubles, same enemies, and more than enough of both. Now, we could circle each other and growl, sleep with one eye open, but that thought wearies me. I don't care what you've done, I don't know what you're planning on doing, but I'm trusting you. I think you should do the same. 'Cause I don't see this working any other way.
You are a healer, or a tank, a crucial member of the team. It is a privilege that you get to queue so quickly (this applies even more to tanks). You do NOT get to pick who gets healed, you do NOT get to 'accidentally' let one mob run by, and let people die. If you signed up to be in a role, you better perform that role, unbiased, no matter how much of a jerk that hunter is, or whether or not the mage won't switch out of his PvP gear. It is your very own Hippocratic oath, one that you signed by clicking that little check box next to the plus symbol with the 'Healer' text below. Don't be an idiot about it.
4) There is a following, very fitting quote from Simon's sister, River:
River: Also... I can kill you with my brain.
Just because you cannot be an arbiter of life between your party members, you still do have a voice. First, if someone is being extremely offensive, there is the Ignore button, as well as the 'Report to GM' button. Both are viable solutions for most of your troubles. However if their conduct falls outside of the realm of the little chat box int he bottom left corner your screen, then you have the 'Vote to Kick' button in your arsenal. If one person is really bugging the whole group - through offensive actions, AFKness, DC'dness, or other general ruderies, then do the vote and remove him from the group. A few rules I follow when dealing with the 'vote to kick' function:
- First, if someone has said they will be afk for under 3-5 minutes, I won't kick them. If they don't return by then, I feel totally in the right to do so.
- If someone is taking too many afk's, then I feel I am in the right there too. It depends on the length and number, but most often people find themselves agitated after 2 or 3.
- If a person doesn't tell the group they're going offline, and they're gone for over a minute and a half, I usually send out a vote.
- Lastly, if someone is attacking another person verbally, or being purposely offensive, they will earn an immediate vote from me.
Remember, these are my own guidelines, and you by no means have to follow them - but it IS a good idea to figure out what yours are, so you can be consistent about them. Lastly, each of these simply votes for the individual to be kicked, and if someone knows more than you do, they can decline and inform you of the reason for the DC, or the number of AFKs, or an assurance the rudeness will die down.
5) Lastly, you really do have a powerful weapon at your disposal. Your final option is to quit the group, but this power should be exercised with extreme caution. Tanks do not get to drop group because CoS starts with a 5-minute speech. DPS can't call it because they hit FoS and actually needed 5 badges instead of 4. Healers can't immediately drop group when you see that the rogue has two trinkets from level 70 brewfest. You have an obligation to stick around for at least a little while, because you signed up for it.
The dungeon finder has a great option, letting you NOT pick a random dungeon. Also, you can just run with guildies or PuGs from your server, and not use the tool at all, to avoid potential conflicts - you can even select a random dungeon and get your daily frosts that way. However if something truly unexpected and intolerable occurs, and you feel that it is time, do not hesitate to drop group. Just remember, with great power comes great responsibility. Yea, I just went there.