Organize your ideas on scratch paper before you begin writing. Write what is most important first. An excellent four-step strategy is described in How to be a Successful Student by Donald Martin. They are not a measurement of your self-worth, creativity or of your intelligence. If the very idea of taking a test causes your stomach to get creepy and sweat to pour out of your pores, then it is time to rethink your definition of a test.
Evaluation is a feedback mechanism that implies purpose and progress.
The true purpose of evaluation is to determine your strengths and weaknesses, what you know and don't know, so that you can make adjustments in your study habits to benefit from or build on your strengths in order to improve your weaknesses. Take time to assess and make adjustments to strategies and goals. Evaluate frequently to see where progress is being made. Make adjustments where indicated. Look for mistakes in grading.