What I do to be a good student and be prepared for every test and exam is to relax, with exercises, breathing or music. I've discovered that relaxation has improved my memory, creativity and learning abilities.
This is my favorite relaxation book The Secret Art of Seamm Jasani: 58 Movements for Eternal Youth from Ancient Tibet, whose special movements and exercises let me relaxed but active, revitalized to go ahead with the study. It gives me, in one word, energy!
The other very useful stuff is to listen to some very good and relaxed light music, such as The Book of Secrets