A good way to pass an exam is to work every day. You may not pass an exam if you don't work hard for most of the time and then work hard only a few days before the exam.
If you are taking an English exam, do not only learn rules of grammar. Try to read stories in English and speak English whenever you can.
Before you start the exam, read carefully over the question paper. Try to understand the exact meaning of each question before you pick up your pen to write. When you have at last finished your exam, read over your answers. Correct the mistakes if there are any and make sure that you have not missed anything.