get yourself in a state or situation that relaxes you, i did most of my studying before my final exams at my grandmas place, because i felt calm and safe there, for you it may be something different, or it may even be a state of "mind", like maybe a few beers or something illegal will help you, im not judging you, exams are stressful, heck i moved in with my grandma just to concentrate.
but find out what works for you, cause you wont be able to remember anything if you are stressed out while studying, you will end up rushing stuff and not taking the time to understand what you just read, and mix that with the stress you will be feeling once you stand there in front of your teacher, or sitting at the table, and you will freak out and make some stupid mistake.
EDIT: oh and i also smoked 2½ packs a day while studying, it gives you cancer, yes, but it calms you down.