How can I build some discipline to help me focus more on school work?

Browsing Reddit, Facebook, and my RSS Feeds is often far more compelling and relevant to what I'm interested in than sitting down with my history book. As a High School student, I still manage to get good grades, but I never feel that I am truly learning the material as well as I should be or as interested in it as I'd like to be. What are some tricks I can employ to make myself more studious?