The best way to get into West Point is to have the qualities of the kind of individual they are looking for - namely being a scholar, leader, athlete.
Take the correct courses to prepare you for West Point's rigourous curriculum. Challenge yourself academically with your core courses in English, History, Science and Math. If you can, aim to take calculus in high school and make sure you take Chemistry with a lab and also preferably Physics. Cadets at West Point also take foreign language. While it isn't required it is beneficial to take 3-4 years of a foreign language.
Participate in athletics, team sports are great. Shoot for making Varsity and provide leadership to your team.
Leadership activities - these are many and varied depending on each candidates experiences. If you want some military exposure and JROTC is not available seek out Civil Air Patrol or Sea Scouts.
Soldier532 - I am not trying to discourage you just make sure you are making an informed decision. Military school, West Point included, provided a structure and discipline that is very difficult to live with. My concern is that after 2-3 years at a military high school you will realize that to go to West Point you will have to sign on for 4 more years and lose your enthusiasm. There is a sacrifice - to your social life and life "on the outside" in general.
Talk to your parents, your guidance counselor and the folks at the school. Ask them if how many cadets have applied, received appointments and gone to West Point.
Go to:
http://admissions.usma.edu/startyoung.cfm
read through these pages and get on the mailing list. Apply for the West Point summer seminar in your junior year.
Good luck and keep studying!