Sleep is very important, get atleast 7-8 hours, be relaxed, dont be tired.
Read each question carefully, dont spend too much time thinking, start writing, the thinking will take over by itself from there, with multi choice go with your first gut feeling as it's usually right, change it only if you feel the need to, if it's a science exam dedicate 1.8 minutes per mark to the written answers, and fill the criteria for answering each question.
Finally: It's not the end, good luck!