Just saw a good article by Lee Jones at cardplayer.com about common mistakes players make in NLHE Sit and Go tourneys. If you are somewhat new to NL and/or Sit and Gos, check it out, there's some good advice. And if you are new to Holdem in general you should start with Lee's book Winning Low-Limit Hold'em, which is generally agreed to be the best beginner's book on the subject available.
I'm actually working on an article about NL cash games, I'm about 80% of the way through the rough draft. I'll post the article here when it's done.
Ted