To have the best shot at an appointment, you need to do three things really well.
First is academics. You should take the highest level math, science, English, and language classes you can handle. For example, as a senior, you should take Calc, not Algebra II or Pre-Calc. Getting As and Bs in these classes is a good thing. Given where you live (No. VA), you want to score around 1350 on the SATs. If you aren't naturally a good test-taker, start preparing early.
Second is athletics. Start with what you like. Team sports are good as are sports that involve running. If you can do varsity, that's great. If you can't, you can still participate. Sports such as martial arts, golf, skating, skiing, cycling, etc. are ok but not as good for USNA. I'm NOT saying that you won't get in if you participate in those sports, just that they tend to be solo (vs. team) activities and harder for USNA to measure excellence.
Third is leadership. You don't have to be leading as a freshman. The best way to approach this is to find a handful of activities that you enjoy. They can be in or out of school. Examples include student gov't, school clubs, church activities, scouting, or community activities such as working with Big Brothers/Sisters, animal rescue, etc. What is important is that you enjoy the activity and feel passionate about it.
As you spend more time with that activity, leadership should come naturally. It can be "formal" (i.e., club president) or informal (starting up a dog rescue in your neighborhood). The key isn't so much the title you have but what you actually do. You can be president of a club and do nothing or be just a member that is responsible for many things.
One final comment . . . you will be much happier in h.s. and in life if you focus on doing things (activities, courses) you enjoy rather than what will get you into USNA or other SA. IOW, if you play the cello and really enjoy that, don't stop b/c it's probably not going to help you with USNA. Mids and officers have lives outside of their military responsibilities. That said, you also have to buckle down and do things because they're "good for you," like taking tough courses and studying. It's a balance.