The goal of test-taking is to try to show as much of what you know. That is the best you can do. Your attitude can be greatly improved by exhibiting the habits of good nutrition and exercise, as well as by getting plenty of sleep the night before the test. Reward yourself after the test go to a movie, hang out with friends, have some fun. Do something relaxing the hour before the test.
Last minute cramming generally increases unnecessary anxiety.
Plan to arrive at the test location early this will allow you to relax and to select a seat located away from the doors, windows and other distractions. Avoid classmates who generate anxiety and tend to upset your confidence. Begin to organize your time efficiently. Work on the easiest portions of the test first. For essay questions, construct a short outline for yourself, and then begin your answer with a summary sentence.