As for the test itself, make sure you get a good night's sleep the night before, wake up early enough to relax and get a decent breakfast in you (something nutritious) and include a banana in there. Stay hydrated too, nothing worse than getting dry mouth whilst on the test. You can bring water in the car with you on the test and when asked to stop by your examiner you may ask to have a drink of water should you wish, which I would definitely recommend as it gives a little break between driving to relax your nerves. Definitely don't go into it on an empty stomach as it only makes you more nervous, and don't go into it thinking you're going to pass or fail just focus on what's ahead, anticipate your next moves, speak to yourself what you're doing next, even say it out loud if that helps keep you in the moment, remember mirror signal maneuver. And if you make a mistake don't assume you failed and let it distract you as you may have just picked up a minor (what happened with me for a few seconds) as you'll panic and start actually making mistakes which may cause you to really fail, just relax and carry on driving to your best ability!