A lot of the following is advice that we received when we first started at HLS and some of it we learned along the way.
First, some practical advice. Buy your casebooks used, figure out which courses permit laptops for note taking purposes, and schedule your meals around lunch talks. Do your best to stay organised. Start a system early and try to stick with it, but whatever you normally do to keep your schedule, find a way to make note of personal and academic deadlines all in one place.