I did AQA Physics and Chem and got >90% and best in school for both, so I must have been doing something right!
Essentially, make sure you understand everything in the lessons. I mean everything. and I mean understand. If you don't, get it sorted.
Flash cards for definitions, formulae, and equation sets (e.g. for Chem) are a godsend.
Past papers will be your best friend, but don't do them too early.
For Chem, past papers have harder questions as they are more unstructured (ie 1990s). These are good prep for Section B. Definitions are easy marks, as are calculations and mechanisms, as they're all just memorising.
For Physics, past papers are key. Mechanics 1 from Maths will help with the mechanics side (inc suvat). All I can advise is past paper questions. Write out all possible answers to the long 6 markers (e.g. double slit, stationary waves, young's modulus experiment).
For ISAs, do ALL past papers.
For Maths, I did AQA so I don't know how relevant this is, but again, past papers were the only revision I did, and ended up getting 98%.
I cannot stress enough the importance of keeping up with notes in class, thoroughly understanding everything, reading around the subject (esp Physics) AND GETTING A GOOD REVISION GUIDE.
I used the Collins ones for sciences, but they are occasionally inaccurate. Best to get two to cross reference- I also had the CGP ones.
Good luck