Read the book/notes (if made by the teacher) over and over. I then write down everything I remember, and check with the textbook/notes. I repeat the process 4 times or so. I hardly do past papers for biology. Maths I do every single exercise in the Oxford and Edexcel official textbooks. I then try to do every single past paper in 30-45 minutes max.
I tend to write notes using the textbook. I usually don't really re-read these notes but I find that by writing the notes it helps me to take it all in. After this I'l read through a revision guide before moving on to past papers. It may be helpful to know that i only do science subjects (Chem,Physics and last year Biology) and I don't think this way of revision would be as effective in other subjects; Maths for example where i find doing plenty of past papers to adequate.
I read my notes then read the textbook. Make more notes. Complete practice papers under exam conditions. Find where I went wrong in the past paper and revise the subject areas. Make more notes. Read textbook again. Complete more pass papers until you only get a few questions wrong. Seems to work best for me.
I copy out the revision guides over and over again. In the last week before the exam I'll do a lot of past papers to get a feel for the style of the exam and what questions typically come up as well.