Exams are an unpleasant part of life and can be very stressful. So how do you stay sane and do your best?  Reachout.com have some tips including:
Manage your stress - plan your revision and break it down into manageable chunks;
Take the pressure off - if you're putting too much pressure on yourself try to remember that failure isn't fatal and if others are putting too much pressure on you (e.g. parents) try talking to them;
Do it together - study with a friends who take the same subjects;
Go easy on the substances - caffeine, red bull, (avoid drugs and alcohol altogether);
Get enough sleep, eat good food and keep moving; and
Have a back-up plan - if you don't get the grades you need have a plan B.