ranks (names and what they look like), general orders, learn as much as you can about the m-16 and a bunch of other stuff too if you want. Its just that the general orders will probably take up the most time to memorize out of everything so get a head start on them. And the ranks you'll want to know because you're gonna want to properly address the person who is about to rip you a new one. Aside from the inprocessing staff, you are gonna get screwed with for calling someone by the wrong rank. Also on your GMS1 exam, there are some questions about ranks and it will save study time.
As far as studying and preparation goes, you'll hear a bunch of crap from people about how you dont really need to study for things and you dont need to prepare as much...I would say the best thing is to be as prepared as possible. Plan on studying everyting you learn. Once you get there and get into the pattern of things, back off on some of the stuff that you think you dont need to study/practice as much. Its all on you and everyones different.
