Learn all the basic math.
odds to hit flush draws, straight draws, sets etc.
If you're playing online make sure you get either pokertracker or hold'em manager.
Analyze your game and plug your leaks.
Think about the game all the time and consider what your opponents are doing and how you can exploit that.
Sign up at a poker training site. There are a ton of them. My favorite is runitonce.
Get a poker coach.