The best thing you can do is crap your self for a few hours before hand and then shut up jump in and just DO IT! Make sure you have your weight and balance, weather, PLOG, walk around etc done.
There is some allowences for failure. If you muck up your PFL and miss the field make sure you nail the gliding landing from the circuit. If you mess up just admit it. I did my PFL but messed up my gliding landing. When it was obvious I admitted it, my examiner did a quick go around, demonstrated it and then I did it. When I was about to lift the flaps for the touch and go he took control and told me I had passed.
Remember just dont get cocky, do have a polite conversation while your flying but fly the aeroplane first.
Good luck mate.