Don't cram your head the night before the exam, digest your new knowledge slowly, over time.
Plan what you're going to study and when. Stretch it out, make sure you really understand the content
Reward yourself, during a break get a snack, watch a show, or surf the net...
When you study, ditch the library and head to the coffee shop, or park, etc.
Plan breaks
Review class notes within 12-24 hours of exam
EXERCISE - It helps boosts the attributions of the studying
Give yourself "pre-tests" or mini-quizzes you either make yourself or find on the internet related to your subject
Check your surroundings, they can have a HUGE impact on your concentration levels
Chew a new flavor of gum while studying, then chew it during the pre-test, and then the actual exam. Your mind will associate the flavor of gum with the study knowledge.