1. find out whats going to be on the exam. What the papers going to be like,what sort of questions/topics will be asked etc. If you have past papers you can find this out from there.
2. Go through the paper/topics/whatever, and work through some practise questions for things like math, science etc. or making/reading notes on the books/toics for other subjects like english.
3. read through the notes you have, copy them out, spider diagram, revision cards, saying stuff out loud, whatever works for you.
4. Practise answering questons. Either from the internet revision sites, revision guides, question you did in class, past papers, wherever. Or for enlish maybe read through any essays you've done before. otice what you did well/got good marks for, and read any points you could hve improved on. Then try to improve on the points you're not too good on in your revision + exams.
Good luck. I'm sure others will add some more usefull advice if mine was just a load of waffle tho!
My exams start tomorrow. I have the "why didnt i start revising ages ago" feeling right now. Statistics exam tomorrow. Fun FUn Fun.