I have a DS who is a high school freshman. What are the steps to be taken to best fulfill his goal of attending USNA?
All of the academies use a similar formula to determine who receives appointments. Understand the process early on, and focus on the big picture. Although there is a lot of discussion about a lot of factors, some are much more important than others. Your son shouldn't live his life just to get admitted, but he should be sure to work hard, without any low momentum periods, on academics. Most difficult classes he can handle, and he should be disciplined in his studies, not just to get good grades, but to learn the material well enough that he has an edge on the ACT/SAT, tests which he should take early and often. USNA only counts Math and English scores for the ACT. Other academies consider all subscores, but math and English are still by far the most important. The tests scores are, in my estimation, the single most important factor, and a kid can improve his/her superscore by a lot over the course of time with study, and even just good luck.
Encourage your son to enjoy his high school experience, and be involved in a lot; particularly team sports, and student council and/or NHS. Other organizations and clubs certainly count, but those are the biggies. If your son stays involved in those groups he can put himself in a position to become an officer in student council or NHS. President or VP in those organizations score big points. Varsity athletics are very important, and multiple varsity letters in multiple varsity sports should be a goal. If he is able to become a captain, that is huge on the leadership component.
Have him always maintained good relationships with his teachers, which is always good policy, but it could help him later in the admissions process. He should maintain good fitness. And stay out of trouble, which isn't too tough for most of these kids.
I would encourage him to consider other services and academies. They all lead to becoming leaders in our armed forces, and all are exceptional schools. Maybe visit the academies you can get to.