My thermo classes usually had far too many problems for the time given to take the exam. Prep depends on how the prof teaches the class.
If he's doing the "traditional" approach where you go along with history, discovering thermo organically, and doing problem sets, then I would focus on practice problems. This gave me the experience setting up and solving the problems that we had on the exam.
If he's doing the goofy postulate-first derive-all-from-fundamental-truth thing, then you'd be better off crying. Just kidding, study all the calculus and derivations.