Concentrate on the matter in hand. Think about the test route you will be following and the important points you need to concentrate on.
Use visualization techniques to practice driving in your head. Picture yourself performing particular manoeuvres and focus on the points at which you need to turn the wheel, change gear, apply the brakes etc.
Listen to the last-minute advice of your instructor, and don't be afraid to ask him or her for clarification / reassurance on any matter.
If you are driving to the test centre, do so to the best of your ability. Maintain the accuracy and observation levels you have been taught so that you are properly 'warmed-up' by the time you come to take the test.
Just before the test, take a few slow breaths to relax. Clench and relax your muscles to get rid of any tension.
Tell yourself that you can do it! 32 million people hold full driving licenses in the UK. We're sure you can too.