Get a good night sleep before the test. Eat breakfast and bring lunch.
Proper sleep & nutrition wont raise you up-and-beyond you FL average, but you’ll protect yourself against a big drop.
EDIT:
It seems like common sense, but I didn’t do it (and it costed me). Please get a full night sleep before your exam.
Don’t be surprised when you sit down at the computer and realize the screen is slightly further from your face and in a slightly different font-size than you were expecting.