Definately try and learn ICM.
Single most important things I have ever heard are:
1. Every hand tells
a story. Stop and think through that story.
2. If every hand tells a story, make sure you tell a story and stick to it. Even if the story isnt actually what your hand is.
3. If you 2 to 3BB raise with 78s, then you can play it as though it is a good ace on the right flop, or KQ, or a pocket pair, so you can get hands through which are not actually what they are. Hope that makes sense?!?
4. Phil Helmuth once muttered that "you can't go out if you don't put all your chips in". He couldnt be more right. If you want to steal some blinds at 50/100 when you have 3000, why do you need to bet 3000?