Haven't started medical school yet, but I would assume that the same tactics used for group study in undergrad science classes would also apply. I prefer question answer formats because I feel it's a more active process, whether you're quizzing another member, or asking them to explain something you don't understand - teaching the material to someone else is one of the best ways to reinforce it. Granted most of the material is memorized, but you can make it more interesting by picking a process - for example a biochemical pathway, and name the steps backwards, going around in a circle. Or for anatomy, name all the bones of the body going from head to toe and back, in order. Reviewing things backwards is also a great way to reinforce material. If you link things as such in your mind to the step or part before and after it, it easier to recall rather than memorizing it randomly out of order.