As a HS grad or GED holder aiming to succeed in through the 37F pipeline, what areas of study and skills would you suggest I focus/build on?

Being out of school but planning to enlist, İ want to structure my free time to study and prepare myself physically and mentally for OSUT, A&S and the Q-course. I believe my interest align with the job however im not so sure if I have college level aptitude in skills and subject areas required or sought after in the pipeline. Maybe you can give some advice.