The best tip for any revision is to start with the past exam papers and work back from that. Otherwise you will spend a lot of time revising the wrong stuff, or the right stuff in the wrong way.
All past papers and mark schemes are available for free for you to download. You need to know your exam board and specification, but you can start here:-
Edexcel - http://qualifications.pearson.com/en/support/support-topics/exams/past-p...
OCR - http://www.ocr.org.uk/i-want-to/download-past-papers/
AQA - http://www.aqa.org.uk/exams-administration/exams-guidance/find-past-pape...