Learn and revise your subject
Dont study late into the early hours on coffee or the latest stimulant. Studies have shown that you will remember things more clearly and effectively if you revise when you are fresh. Practise bursts of revision. This can mean as little as ten to forty minutes revising. Time yourself and have a ten minute break. Its not always about quantity of revision, but also quality.
Dont drown yourself in a subject, but take it one step at a time. Think about what type of questions the exam paper is likely to ask. Practise with past papers and make sure that you know how wide an area the scope of a subject an exam will cover. Posters, post sticks and flash cards can also play a vital role in revising.