Here is my tid bit of advice...
1) Fitness: Start working out now! IDC how fit you are, there's always room for improvement. You need to be preparing for your CFA. Mine was a very challenging 30 minutes. I've been chubby a my life so it was extra hard for me but I have a friend who attends USMA that was physically amazing and it was hard on him. So do push ups, pull ups and sit ups at least 5 days a week for a minimum of thirty minutes. Also Run your behind off! Not just for the CFA but for USAFA itself. I started with a mile, then a mile and a half, and now I run 3 miles. Occasionally time yourself to track your mile and 1.5 mile speed.
2) Test Scores: These are important because academics weigh the most. Use the scores you have, BUT DONT STOP TESTING unless you are accepted or maxed out (36 ACT or 1600 SAT) trust me on this one. I took the ACT four times! And the SAT twice! I was scheduled to take more but I got accepted. Never forget that they take mixed scores either! My composites on the ACT sucked. I got 25,24,23,24 (in that order) but my highest scores were (Math 25 Reading 29 English 26 Science Writing 25) you are already higher than my SAT (Math 560 Reading 580) so you're on track. I recommend taking both. To people one is easier than the other but you need to take both so you know which one produces better scores. Also take the writing at least once so you can apply to back up colleges.
3) Recommendations: this process requires tons of recommendations so start having some teachers in mind. I applied for 2 senatorial Nominations and 1 congressional nomination which are applications in them selves and required three recommendations each. What I did was picked six teachers and had each of them write a letter of recommendation for my nomination packets and o had four teachers write me letters for USAFA (2 of those will be done online) by the end of it I had extras but more is better than less but only send the requested maximum amount.
4) Find support and don't get discouraged: This is going to be a hard a stressful process. The acceptance rate is 9.9% and USAFA is the 4th ranked university in america (above all the military academies and Harvard, Stanford and Yale.) So its huge. At one point o got discouraged. Never get discouraged! Keep treadi g on and have someone to vent to if you get to stressed.
5) Don't stop fighting till it is officially over: There will be times where you think you won't make it. Every time I took my ACT and my scores went down, I started to think I wouldn't make it. I applied for early action and on Jan 15 they told me I was deferred to regular decision. I was denied one nominaton and got a nomination for a different academy. After all that I wanted to quit. 2 weeks after those negative letters, my congressman calls me and tells me that I have been accepted to USAFA. I promise, that is the greatest feeling you will ever feel and it is worth the fight and hard work so never give up!
6) Keep on the Ball: you're starting as scheduled and that is great! I had no varsity participation and not much going for me so I had to cram a lot into my Junior and Senior year and I didn't even start my application until the beginning of my senior year but I still finished for early selection. That's what you should shoot for, it looks good and they consider that you finished everything early. Take AP classes or honors, get a varsity letter or at least play a sport and find a leadership position to excell in(not just to hold) maintain a good GPA! At least 3.5 mine was 3.7 so not everyone who is accepted is a 4.0 but shoot for 4.0 regardless! Never slow down, just power through the paper work and the challenges! Use your parents! Mine help me so much its unreal! Do things to make yourself stand out!
7) Have a back up plan: If USAFA is number one than go for it head on! But have a contingency plan! I completed my packet for early action which is NOV 1 so I used the extra time afterwards to meet December, January, and February college applications. I Applied to like 10 schools after finishing my USAFA application and got accepted to Penn State so I knew if USAFA didn't happen, I had a great school to go to. At least apply to one school you know you'll be accepted and one that is harder to get into, that's just minimal though.
8) This is the most important thing to remember. NEVER FORGET THAT YOU CAN DO THIS!
I just shot a lot of info at you, I know, but I promise it should help and I through in all my personal examples so you could see how someone has gone threw it. And I did this recently. I'm going into the class of 2019 so you'll be right behind me. I'm sure you can do it and if you have any questions while applying, feel free to ask me!
P.S sorry for any misspellings. Typing on my phone is ridiculous.