I'll tell you the same thing my fellow students and instructors told me the days leading up to my CPL test... "DON'T F**K IT UP!!"...
No, but seriously, don't forget the examiner is to be treated as a passenger as soon as you start walking out to the aircraft, he wants to see you treating him as such even though it does feel awkward. If you have a PPL then you've already passed a test that says you can fly safely from A to B, now your Commercial Test is here that examiner wants to see those same safe flying skills but with attention to the commercial aspects!!
My examiner for my test didn't pass me the first time, reason being? I didn't show commercial considerations, basically he said I didn't treat him enough like a passenger and as such he could see I could fly safely, I only made a few mistakes that would have otherwise been inconsequential but added to that whole non-commercial treatment he couldn't pass me. Mind you, next one was a compelete breeze!!