Prepare beforehand. If you are confident you have adequately studied for the exam, it will be easier to keep calm during the test.
Enjoy a good night's sleep. If you're rested you're less stressed and better prepared to take an exam.
Release nervous energy. Find a non-offensive way to release nervous energy during the test. Pick up a pack of gum before the exam. Chewing gum helps to channel nervous energy. It beats foot tapping and pen clicking. Just be sure not to annoy other test takers by snapping and popping your gum.
Show up on time. Give yourself a little extra time to get to the testing site. Nothing adds to a stress level more than showing up late. You want to make sure you have ample time to complete the test.
Don't get rattled by your surroundings. If the person next to you finishes the test in what seems to be record time, ignore it and remain calm. It's possible that your classmate was unprepared and skipped half the test. Don't let your neighbor's test time add to your stress level.
Practice deep breathing. Taking deep breaths during the test increases the oxygen flow to your brain. The extra oxygen in your brain helps you think better and remain calm.