Academically, you should try to be in the highest level classes you can (usually AP level) and still get good grades.  Math and Science are critical for USAFA.  AP classes are not critical, but they will definitely improve your competitiveness.

As far as clubs and sports, the academies want to see a variety of activities, but it is better to have a few programs where you are a leader, than simply be a member of many programs.

Try to make Eagle Scout, earn the leadership in JROTC, and play sports.