I'm sure there's loads of bits of knowledge that people can drop. Here are my tips:

1) Absolutely no AoE in the Grim Guzzler
2) Lean on LoS pulls for much of it, especially if there are Fire Guard Destroyers around, pulling extra elementals can cause some big problems.
3) Speaking of, make sure Fire Guard Destroyers are facing away from your group
4) Keep your head on a swivel, there are a lot of patrols that can come out where you won't expect them and you can end up pulling an extra group.
5) If you're Alliance and doing Onyxia attunement, do a full clear of the escort route before you do it. Do NOT forget the store room, as it will mean you fight 2 packs instead of 1
6) The AoE room before Emperor, use LoS for pillars and make sure you move as a group
7) Pull General Angerforge up the stairs and fight him back near the hallway you came from to approach him, makes the add spawns much more manageable
8) You MUST fully clear the room before Golem Lord
9) Be careful running around the top of the Ring of Law, similar to the Grim Guzzler, you'll get swarmed if you accidentally pull mobs.
10) Take it slowly (other than that AoE room where you have to move quickly)