Hi Tyler!
First off, the Army doesn't have "boot camp," that's only the Marines and Navy (and Coast Guard, I think?? Someone correct me if I'm wrong). The Army has Basic Combat Training.
To be ready for BCT, you don't need to know ANYTHING. You will be taught all of the basics (if you want a head start, though, join a Junior ROTC detachment and learn ranks and insignia). You don't want to go to a gym. You certainly won't be lifting weights while you're at BCT.
Instead, you want to work on your push-ups, pull-ups, sit-ups, and running.
Work on those until you can do:
60 push-ups in 2 minutes
65 sit-ups in 2 minutes
5 pull-ups
Run 2 miles in 14 minutes
This will make you a slightly above-average recruit. You don't want to be average because then BCT will be harder than necessary and you'll be 3x as stressed for those 9-10 weeks. Aim for honor graduate stats instead: you have at least 4 years to prepare, so why not?
Make sure you remain qualified to enlist. Keep your weight down, don't get in any legal trouble, and keep your credit score good.