Some anxiety about taking tests is normal, but when the anxiety affects how you perform on the test, it is time to build your confidence. Review your skills either by yourself or with another person, preferably a counselor at your institution. Learn how to study and manage your time. Organize your material that is to be studied. Be aware of outside influences that affect performance. Learn from your testing mistakes.

When you are ready to take a test, approach it with confidence. Tell yourself you will do well. Prepare yourself by studying. Pick a good place to take the test. Make sure that distractions will not affect you. Give yourself time for the tests. Stay relaxed. Dont talk with students who are not prepared. Eat something before you go into the test.

As you are taking the test, make sure your read the directions and answer the questions asked. Watch your time. Skip over difficult areas and go back to them. Move around in your chair, but dont fidget. Dont worry about other students finishing first. If you go blank on an essay or short answer test, start writing something on another sheet of paper. It may trigger your mind.
While taking the test, stay relaxed. Dont tense up. Take deep breaths. Expect to be a little anxious, but dont let it control you. Think positive thoughts and tell yourself that you can take the test. 

When you have finished the test, think back over what you did and what did or did not work on the test. Congratulate yourself on a job well done.