I don';t think you can revise without the specifications!You ge tthese by going on the exam boards site and looking for the specification for your subject,it basically tells you everything you need to know.Flick through it,if you know something,skip it,if you don't get a textbook and write your own notes about it, and take in the knowledgfe as well as writing. Then do a past paper, mark it and note down what you're shit at.PRactise the thing you're shit at over and over then do another past paper.After repeating this proces you should be ready for anything!!!! (Y)
Ideally if you start early enough you can write notes on the whole specificatoin,so whatever you don't know in the past papers you can just flick to your notes on and you're sorted.