Yeah, OB/GYN and surgery, and not necessarily in that order, are the worst.
So much of looking good on rotations has very little to do with actual medical knowledge. Much of it is knowing logistics, where to find things, how to find patients' records, how to write orders, etc. Much of it is also knowing institutional protocols - things that don't necessarily have to be done one specific way but always are. It's difficult to learn these things before you're actually on the wards.
Truthfully, you shouldn't worry about 3rd year yet. If you're a second-year, then you've got plenty on your plate with step 1 coming up. But if you insist, then get a pocket Maxwell's, if you haven't already, and familiarize yourself with how to write basic notes, like a SOAP note or a procedural note. And try to learn some basic abbreviations, so when you see something like NT/ND/No HSM/NABS you'll know what it means.