I scoffed at people who instituted one wipe rules during LK because you could essentially complete any heroic with any random bunch of scrubs the LFD tool assembled. This is not so anymore. The changes to tanking and healing have made it impossible to carry 1 let alone 2 or 3 bad players. Cataclysm has been out for 3 weeks. If you don't know the dungeons by now, you probably won't ever. So I'm issuing this list of rules all pugs so you know what you'll be getting in the future.
1. One wipe rule. I simply refuse to try and carry you anymore. You don't pull your weight and the group wipes because of it. I'm out and in another group in 2 seconds flat. No exceptions.
2. Boss Strategies. If you haven't completed every heroic yet, you should definitely invest in some research on the boss fights for each heroic you will be running. I don't have time to explain your role in each and every boss fight. If you don't know your role in a fight, you should find out what it is in advance and should not be queueing for that dungeon otherwise.
3. Trash. I'm geared enough as a tank now that I'm fairly capable to AoE tank roughly any pull in heroics even with a slightly undergeared healer. You don't like this? Too bad. I'll likely be chain pulling too so I suggest you take your mana break when the healer takes there's. If they have mana and you don't, I'm pulling with or without you.
4. Crowd Control. When running with a geared tank, you will rarely need crowd control as the tank can absorb the majority of damage put out by 5 and even 6 mob pulls, but in the unlikely event that some sort of CC is advised for a pull the CC target will be marked with a diamond, a circle, or a moon. If you have any CC available, I suggest you use on said target lest you cause a wipe and be returned to Rule #1.
5. DPS. If you're continually dying on every other pull or even every boss fight, do not expect me to stick around too long. If you consistently prove to me that you fail and are likely to cause a full party wipe in the future, it's likely that you don't deserve to have me carry you and I may potentially leave for no reason at all other than you're not pulling your own weight.
Research boss strats. Understand trash pull mechanics. Assist off of me. CC what is marked for CC and don't break CC. Know your class and your role in the group.
That is all.