Members of Congress don't appoint, they nominate, so, as Boozebin said, you need to know if your Senators and Representative submit a competitive nomination slate or a principle/ranked slate. Either way, the answer to your question is still the same, do everything in your power to be the best candidate you can be. Study for and take the ACT/SATs early and often, strive for the highest possible score. Shoot for all As in the most challenging courses your your school offers, take on leadership positions in and out of school (you are on the right track with being on AFJROTC staff), participate in high school varsity sports, be in top physical condition and practice the Candidate Fitness Assessment, find a passion out side of school (ie community involvement), apply to the Summer Seminar the winter of Junior year, know about the majors and careers available to the SA you want to attend, know why you want to attend and what you want to do after you graduate from a SA. The list goes on and on. There is no magic formula that will guarantee you a MOC nomination (principal or not) or an appointment, highly qualified candidates are rejected every year. There just isn't enough appointments slots to go around, but the Academies have a pretty successful track record of putting together the right mix of appointees to form a class. All you can do is be the best candidate you can be and don't settle for less than your best. Then, its out of your hands and you know you've done all you could do.