I agree wholeheartedly with Peter: pay close attention to people who are GMing you, see what you like, see what you dont' like, and then work to incorporate the things into your games. I have learned a ton, and improved my GMing skills almost exponentially since using some of the techniques of Mark, whom I playtest with occaisionally, and Piratecat, whom I had the pleasure to learn Feng Shui through his game at the EN Chicago Gameday 2.