Some people self prep at one of the few prep schools that allow for USCGA self prep, while others choose to go to a normal college. There are other possibilities which you may research, including enlisting in the armed forces, though none of the aforementioned options guarantee acceptance into USCGA or any of the other SAs.
CGA does value reapplicants because it shows determination and demonstrates that you
really want to go to the Academy. If you decide to self-prep at a normal college/university, you may consider:
1. Looking into universities that are Minority Serving Institutes (MSI) so that you can apply for CSPI in your sophomore or junior year if CGA doesn't work out (more info
here)
2. Enrolling in classes that relate to your declared major (if you declared engineering for your CGA application, don't take an abundance of humanities classes)
3. Getting involved in clubs and seeking leadership roles (like starting study/review sessions for difficult classes, which should also help keep grades up)
4. Staying physically fit for the PFE, and
5. Keeping in regular contact with your AO and sending him/her any updates
There's no checklist that will guarantee an appointment, but try to address the three main parts of a successful candidate: academics, athletics, and leadership experience. Good luck to all!