I do my job well, I know most fights perfectly, I have raiding experience. Since launch I have completed 3 heroic dungeons, every other dungeon I am in is either plagued by lack of Damage Per Second, Lack of Aggro, Lack of AoE Healing (I'm looking at you ShadowFang Keep) or Lack of understanding when it comes to fight mechanics. So rather than completely complain about it if you have a question before a fight, ASK!.
I cannot help you and I cannot explain a fight if you do not speak up and say that you need help. I will be more then willing to tell you every single rotation, priority, etc that your class uses. I have been counting and in 14 queues since the Launch of Cataclysm I have completed 3 Heroic Dungeons and 11 of those either ended in every other person leaving the party after a single wipe or every single person leaving after multiple wipes.
I don't expect you to know everything, But if you don't ask I cannot help you. Below are some ground rules I'd like people to consider using when in Heroics.
Ground rules for Heroics
1) If a tank asks you to CC a target and you can provide said CC (Polymorph, Fear Glyphed, Hunter Traps, etc) you need to do it, no if's and or buts, generally doing this lowers the amount of incoming damage or makes a fight easier to handle Threat wise.
2) If you are thinking about leaving a Heroic Dungeon and you are a healer, tank or DPS and you will be causing the group to disband please consider staying in the group so that DPS like me do not have to waste another 40 minutes sitting in a Queue - not only is this wasted time for me (40 minutes for original queue, 40 minutes for additional queue you're forcing on me) this isn't a nice thing to do.
3) If you don't understand a mechanic ASK.
That is it really. Rant over!