Take the hardest classes you can. Whether they are honors, AP or IB. By the end of your senior year, try and make sure you've completed at least calculus 1, physics with labs, chemistry with labs and advanced composition courses. Do especially well on those courses, as West Point pays special attention to them.
Remember too, that they like well rounded candidates. They don't care if you have a 4.0 GPA with all APs, unless you have solid extra curricular activities, they won't be interested. This means that although you should definitely push yourself academically, make sure you have enough opportunities to work in your community and participate in sports.
Best of luck! Keep your nose clean and work hard!