I can only speak to AROTC. The application will open the middle of June. That is when you can start working on your application. What you can always be doing is working on taking, or taking again to improve your ACT and/or SAT. For AROTC, the first board does not meet until October, so that means you still have time to take your tests this summer and will have them back in time.
Another thing you can do is set up a visit with schools you are interested in and also to meet with the ROO (Recruiting Operations Officer) for AROTC. You will learn a lot about ROTC, that school, that particular program, and it will help you determine which school feels right for you, and even help decide if you want an Academy experience or a civilian college experience.
Good luck and keep us posted!