What is your age?  What have you done so far?  Realize that most Academies have over 10000 applicants each year and only select 1200-1300.  Most classes graduate between 800-900.  The competition is VERY stiff.  You must do VERY well in school, do well on the ACT/SATs, be involved in your school (gov't sports extra activities), but grades is the most important.  Vol service?  Boy/Girl Scouts or CAP... all could be factors.  Military prep school?  Or any leadership opportunities - grab!