don't be stupid like me and leave revision to last minute, do this at gcse and get all your As and A*s, try it at A level and leave the exam room crying! one thing i think is important is making sure you actually understand what you're learning, no point trying to remember things word for word (except definitions), if you listen to teachers in class and understand the work then you should do fine, defo revise early or you'll end up like me with sleepless nights drinking black coffee while speeding through pages of boring information the night before the exam. *sigh*
AND OMG DO PAST PAPERS ALWAYS! AS MANY AS YOU CAN!! THEY REPEAT SO MUCH (well i can only speak for ocr chem, bio and mei maths but i'm sure it's the same with most exams)
also being an organised person is helpful. i'm not, so it's a good thing i don't rely on my class notes, if i did half will be missing and i will be dead.