Are you in year 12?
I just started year 12 and i am doing ocr computer science as well
I have not got the textbook yet but for now i am going through each point in the specification and making concise notes (Usually through a mindmap)
I think with the textbook it is best to make flashcards from it
Also once you are done with a topic and start revising from it make sure you understand every point on the spec for that topic (If you are unsure consult with your teacher or watch a video from computer science tutor or CraignDave)
Good luck with your studies