And my advise would be to Make a checklist and colour code the topics in different colours. Green for the ones you have mastered, orange for the ones your ok in, and red for the ones you dont know.
Go through the red ones first, the orange ones next and the green ones at last.
Use flashcards and go through all of the past papers.
For math I assume you will be doing edexcel mths and I would advise you to go through all of the topics and revise as much as possible. Practice is key