The best thing is very simple and significant. Apply and get all info in ASAP.
With rolling admissions the statistical chances of appointment, all other things being equal, are better earlier, worse later. So git 'er done ... as early as possible which is different than as soon as possible. Early is the USNA calendar, soon is yours. Use theirs. All the rest is pretty much outta your control. This is not.
And btw, if all your things are NOT equal to (or better than most per the profile) all the more reason that earlier is better. Shows lots of genuine interest coupled with motivated behavior.
The "worst" thing ... not having TWO courses in calculus, with A's and maybe an AP score of 4-5 or an SAT II score of 700 or so to show you know. If you've but one, you've still time.
Also, in asking this question of several other current mids, they ALL mentioned writing more. So that said, you may want to go to the site of a retired Navy captain who has written MUCH of the Navy, including the USNA classic "The Return of Philo T. McGiffin" ... David Poyer. He has some excellent suggestions on learning how to write. But this point has more to do with STAYING there vs. GETTING there. His most powerful suggestion though, again, for which you've some time?
Read as many of the great writers as you can. And one adequate writer, Smallwood's book on USNA getting in and staying in.