I'm doing my GSCE's too
Just got Maths and History left!
Personally, I'm awful at revising, but then I'm always quite laid back about my exams. Everyone is different, but i know for me I can't just read a revision guide and expect it to sink in.
I make my own revision pages by looking at the information I need to know (either in my school books or the revision guide) and putting it in notes/lists/diagrams
This way I can make it colourful and easy to remember, you can relate a certain subject to the way you laid it out on the revision page. I also feel calm doing it this way, as I don't have to panic trying to answer practice questions I don't know.
Also, it helps if theres a technique to the questions in the exam, to draw out a structure of how to answer each question.
Best of luck x