Once you're in the car, wait for the examiner to let you know about the test procedure. In a nutshell your examiner will be letting you know that he will be giving you directions and unless he has asked you to do otherwise, you should follow the road ahead. Your examiner will be quiet for a good deal of the test, this is not to try to raise the tension, it is to let you concentrate on your driving.
It is easy to let your nerves get the better of you at the start of the test. Your instructor will have given you lots of advice and tips to help you remain calm - now's the time to put them into play.
The next thing to remember is your cockpit drill (D - SSS - M). You'll have done this on every lesson so just relax and stick to the drill as you have been doing on your driving lessons.
All that remains is for you to do exactly what you've been doing on your driving lessons leading up to your test.