When setting a test date and look up test centers at www.mba.com/mba/TaketheGMAT, keep in mind the following:
Consider the times of day you tend to be able to concentrate best. Take your test in the morning or afternoon accordingly.
Make sure the week before your test day will not be a stressful one. This will help you to concentrate, be well rested, calm and in the right frame of mind to ace the GMAT.
Be aware of application deadlines and do your best to provide yourself with enough time after the exam to focus on the other parts of your Business School applications.