Having done mine fairly recently, I would say that it helps to remember to do a few little things that give the right impression earlier on. I'm not saying that cleaning the windscreen, making sure the examiner sees you obtaining NOTAMs or asking him to test his brakes will get you an automatic pass if you're an unsafe pilot, just that it sets a good tone for the test. Also it helps you relax into the role of pilot and makes you less likely to do something daft because you're aware of being an 'examinee'.
I would also recommend practising a few circuits before s/he arrives so that you can get used to the conditions and the problems they present. There's never a perfect day; for me it was totally windless and hot; great for diversions but, despite spending 30 minutes practising them, I had to go around from my first attempt at a flapless landing. Luckily I told him exactly what the problem was and got it right the second time.
Finally, I got some hot tips off students who'd recently done it about what the examiner's latest foibles were - favourite routes, maveuvre's etc. which definitely came in handy.
(Disclaimer - though of course you can never be certain...!)
Good luck - I really enjoyed mine in the end!