On breaks, reward yourself for work well done. Following this pattern can enhance studying. Coffee or other caffeine or high sugar items only have short term benefits. At exam time, it is particularly important to maintain a balanced diet. While a piece of fruit may give a quick burst of energy before a test, the best aid to effective study is a balanced diet.
Adequate sleep is also important.
People who are well rested are better able to function during tests than those who are tired. The most important element in determining whether or not you will do well in a testing situation is understanding test directions. Listen to and read all directions before answering any test questions. Now, before actually writing down anything, read very quickly through the entire test. You want to know how many pages are on the test and what the point values for each section are.