1. Have discipline
Know when you are beat.
2. Risk reward
Try to risk as few chips as possible in order to win the maximum amount.
3. Be aggressive
Passive players cannot win. You must be aggressive. You must be the leader in a pot and make other people make decisions.
4. Stay focused
What is your goal for the day? What is your goal in this tournament? Ask yourself and find the answer.
5. Have a routine
Follow your routine through every hand, every day.
6. Know your bankroll
Don't play beyond your financial limits.
7. Understand your limits
If you are in a cash game and you're the sixth best player in the world and you're playing against the top five, you're in trouble. At least try to play against people that you can beat.
8. Don't bluff the unbluffable
Self-explanatory. Boy have I made this mistake many times. Avoid it at all costs.
9. Mask your pain
If you are going to slow play your big hands, be prepared to release them with minimal pain if it backfires, and nobody needs to know what you have done.
10. Go with your gut
Trust your first instinct - you'll be right 95% of the time.
11. Enjoy it
It's a game and you are supposed to enjoy it!
12. Poker is not a game of luck
On any given day, luck is a huge factor, but over the long haul, the better player is going to get the money. This game is 90% skill.