If there were any sections to start looking at beforehand, I would recommend the flexors and extensors of the arm, as well as the muscles of the thigh and leg. Hands and feet included, they can also be a bit tricky. All of those would hopefully be standard fare for any med school anatomy course. Nerves and cardiovascular are pretty straightforward, but it never hurts to put a picture of the brachial plexus above your desk. Skeletal is the easiest, imo. It's the muscle origins and insertions where you can lose yourself.
I'm starting my PA program in a few weeks and Advanced Anatomy will be one of my first courses. I did well in my undergrad Anatomy, and landed a paid gig in their anatomy labs. But I've been studying all summer to get ready for my second round. I know that you always hear the rumor that 'med schools don't want you to have learned anatomy until you take it with them', but as someone who's had some experience dealing with the subject matter, I don't see any harm in beginning to look into something that you're going to be dealing with for the rest of your natural life.