(1) Learn intensely the night before
There are various study and revision guides that will tell you to wind down the night before an exam or just to study key points. Actually if you get the adrenaline flowing and study really hard, trying to read as much as you possibly can and going over your notes in as much detail as you can the night before, this is the best way to stuff more information on your mind to leap out of your brain quickly and onto the page in the exam. The singlest most important tip to doing really well in an exam is to work really hard the night before.
(2) Get a good night's sleep
Tough if you don't sleep well, but be sure that you don't stay up late but go to bed at your usual time. Try not to think about the exam. Again that's easier said than done. If you are a good sleeper then you have a real advantage with morning exams over those that find it hard to sleep when nervous.
(3) Eat breakfast
Make sure that you have food before an exam. This helps you to concentrate and can be worth an extra few marks over the course of an exam.
(4) Revise actively not passively
This simply means actually set yourself little questions to answer. Easy to do with maths, but with other subjects too simply make yourself list for instance five characteristics of life. Doing this helps to find gaps in your knowledge and reinforce what you already know. Just reading a textbook is not very effective.
(5) Do past papers
Test yourself against past papers to get used to the exam format, the style of questions and see how your knowledge is progressing.
(6) Read the syllabus
As part of your revision read the syllabus where relevant (GCSE and A-level exams for instance). Note the keywords that they use for the topics. When revising and doing practice papers try to get in all the keywords that you can: these get ticks and ticks mean marks. Many examiners appear to look for certain words in an answer and tick those.
(7) Pay attention the whole year
OK this is not specifically a revision tip but the whole point is that you are revising what you know, not learning something for the first time. If you pay attention and work steadily over the course of the year then you will find revising easier because you are getting re-familiar with what you already know.