The above is very true but for a second run on an appointment you have to approach it as a military operation and strengthen your weak spots and enhance your strengths. There are two areas to attack: the nomination and the Academy evaluation (i.e. were you 3Q'ed?). For the nomination, I'd call the head of the staff of each congressperson whom you interviewed with. I would thank them for the opportunity to interview and express your desire to apply again next year and ask what could you do to become a stronger candidate. I'd call your Academy RD and your BGO and ask the same question. If you were not 3Q'ed especially try to find out where you fell short in the competition. With this operational Intel you can plan your upcoming year to eliminate your weaknesses and enhance your strengths.
While a good prep school is a good move, remember it is your performance in class that is what counts, not the place you go. The Academy clearly states that for a second application a candidate should go to a 4 year college and take courses that mimic Plebe year. They want to see how you handle Plebe courses with no military pressure. If you need academic prepping, that is what this summer is for. Plan on an English writing course as you must show a level of sophistication and maturity in your essay and interview that makes you stand out from the garden-variety high schooler. Needless to say, "C's" are unacceptable and "A's" and "B's" make the admissions board sit up and take notice. If money is a factor, have you not applied for NROTC? and if not, why not? Even as a non-scholarship Midshipman the unit will give you experiences that you can point to in essays and your next interview. Stay fit in intramurals or some sort of physical sports, ace the CFA, and find an extracurricular activity you like that you can show some leadership in, if not NROTC. Remember this all takes place your very first semester at school. You do not have the luxury of the "college experience" of parties, booze, sleeping in, skipping classes, hacky sack on the Quad and getting F's on your first tests (ah, English...). You need to hit college like a laser from day one. If this all sounds overwhelming, it is no different than Plebe year.
The one thing NOT to do is enlist in either the Reserves or Active Duty. In order to be an officer you must have a college degree and enlisting does not get you that and, in fact, slows you down and makes your chances a lot harder for no reason. Even the Reserves will eat up your time unnecessarily---you cannot afford one weekend a month away from your studies. There are numerous threads here on this very subject. Good luck to you as you can do it-----just like the hundreds of college students who get appointed every year.