Take a full A&P course; most schools that I've seen offer a 3 term/2 semester course that starts at the cellular level and works up to cover the entire body; that's what you want.
If your school offers it, a medical terminology class is nice.
If you can find a school that also teaches RN's, RT's, ultrasound tech's, x-ray tech's, etc, look into the curriculum for them. You probably won't be able to get into the core classes, but see what else is required. If there are some basic health courses...take them. Any classes that cover (in broad, general terms) sports medicine, rehab or nutrition...take them. Basically, see what other professions are doing, and follow along.
Sociology and psychology classes are more than a nice to have; if you pay attention they will be worth their weight in gold in the long run. Given that both have a large part in what we do...good stuff. I'd start with a basic introductory class in each, but branch out into relevant topics if you can; some schools have a variation of the course "on death and dying," or "crisis intervention and management," that would be worth it.
Most importantly, keep in mind that what you will learn in paramedic school is not all there is, not enough, may be outdated by them time you are done with class, and if not, WILL be outdated someday. So...keep learning. Dig deeper into pharmacology, ecg interpretation, pathophys, acute and critical care, primary care...and keep up not only with what is happening with EMS, but with the medical field.