Mate, in addition to the very important technical tips you will recieve from others, let me suggest the following:
Your examiner wants you to pass. He is not an ogre. It is OK to make some mistakes, inform the examiner as soon as you can. He will have noticed. Consider the mistakes on the ground and under no circumstances allow them to get in the way of the rest of your test.
Finally, arrive at the field in plenty of time.
Good luck.
Wombat