You enter an instance using the LFG tool. After the first pull, you know this is going to be a real bad experience. Some signs:
- One of the dps pulls.
- One or more of the dps don't attack the skull.
- People stand in the whirlwind.
- Nobody (except possibly you) interrupts enemy spellcasters.
- The dps don't burn down adds when it's an important boss mechanic.
- The dps deals less damage than the tank (on a non AoE-fight).
- People randomly goes afk, without a single word.
- People refuse to CC.
- ... or worse: People AoEs, thereby breaking the CC.
If you've ended up in one of those groups, and you happen to be healer or tank, there's something you can do about it.
Sit down. Tell the rest that you refuse to heal/tank if people don't start doing their job properly. Tell them what they can do different, keeping it very concrete. Be polite, but firm.
You are not polite if you just play along and try to heal or tank and build up a lot of frustration because people don't care about the fight mechanics. You just burn yourself out.
You will experience a lot of nerd rage this way. You may even be kicked from the group. But as long as you are polite and say what should be done, most people will recognize this and behave. In many cases, you get to kick the worst offenders.
You are a vital part of the group. It's about time you demand the respect you deserve.