Do you play cash or sit and go?
Edit
I guess that doesn't really matter.
- Patience is key. Don't start playing **** hands because you're being dealt rubbish. You
may hit that full house with 2-7 on the flop but in the long run you're going to be down
- Complement bad play. Yes it is annoying when some fool hits the nuts from a retarded chase but it happens. Congratulate him on his excellent play and hope he continues with it.
- Don't play when you're drunk (for high amounts anyway) or tired
- Automatic hand analysis tools are very handy; I can hook you up if you like
- Always bet into timid players to try steal small pots; it does add up

Be cautious of aggressive players but have some balls or you'll get played for a mug.
- Never chase; play by pot odds and good judgement.
- Watch the game even if you aren't playing a hand. You need to know how players react in certain situations so you can exploit their weaknesses.
The most important tip; don't bet with more than you can afford to lose
I'll add some more as they come to mind.