Patience. Be patient and take your time. No need to rush, do not take unnecessary risks. Even if you think "Ah, I could've gone then", it's better to demonstrate to the examiner that you are aware of any potential hazards & can respond accordingly.
It's only 40 minutes, less than a normal driving lesson. Keep calm, focus and just drive. Oh, and keep your eyes in those mirrors all the time. A lot of minors come from not checking the mirrors. Good Luck!