Best advice I've ever had was from someone just before I took off, and it was "Don't eff up"
I've since found out that an EasyJet friend writes DFU this at the top of a pre-landing brief in respect to the same phrase, and another friend recites it as a mantra in more challenging conditions.
It's worked for me every time. I think it has to do with reducing all of the million things that people get stressed over to simply "messing up", and that's only one thing to worry about...
Don't forget you won't be put forward for the test if your instructor didn't think you were ready, so you can do everything on the test perfectly fine. In order to fail you have to give the examiner good reason to fail you.
Good luck!