I second the nomination of Skidkid's. Physical prep is astronomically more important than academic. Your body gets worn out far more - and with less chance to recover - than your brain does. How do you get more rest? You show up with a 300 PFT or better, and able to do 50 pushups at a stretch, and the stress of the place won't phase you nearly as much as it does most others, allowing you more energy to study, which in the end equals less study time. Don't even worry about General Orders and rank structure, that stuff gets pounded into your head to the point of nausea and beyond.
If you want to study something, find [search] the Six Articles of the Code of Conduct and memorize that... but do it between sets of pullups.