For the sciences, I really recommend:
1. freesciencelessons on YouTube: He's honestly a lifesaver. At the start of Y9, I was quite lazy when it came to revision, so I got 2, 3 and 4 in October of Y9.
That was a sign to me that I needed to put effort in, so I used him a lot for my Jan and June tests and ended Y9 with a 6, 7 and 8. Finished with 9,9,9 in Y11, so I can vouch for him. Everyone has their own way of revising, so you should mix and match techniques to find what suits you, but what I did was use freesciencelessons alongside:
2. Exam questions, especially Exampro. You'll learn to realise that there are patterns in answers for science (and Maths). Make sure you mark your work afterwards with a green pen and find what key words are needed.
3. Blurting (
https://www.youtube.com/watch?v=CgrCo1J9A44) is really helpful for content-based subjects in particular, but it works even with English Lit for me. I did this on the days leading up to a test (still do for A-Levels).
4. Topic checklists. I used the ones in the CGP books for each chapter and answered the questions, usually the night before, and then checked my answers.
5. Get on top of your flashcards early. Don't make them too wordy. The best way to make flashcards is to have a question on one side and a brief answer on the other. Use mark schemes and past papers to find the best answer that scores all of the key points needed to get full marks. You can make online flashcards on Anki or Quizlet if you want to continuously edit your flashcards with updated information. Alternatively, if you want to buy some good online ones cheaply, I used these (because I left making flashcards for science too late lol):
https://www.keycardsrevision.co.uk/ For Maths:
1. Maths Genie questions. He also has solution videos and higher-level questions to challenge yourself.
2. You don't have to spend money to access practice questions (as there are so many online, such as PhysicsandMaths tutor, Corbett Maths and Maths Genie, as I mentioned), but, if you want and can afford to, maybe get a good textbook full of exam questions (and exam papers also work). I used this one specifically because it had hard questions in it and answers at the back:
Maths for GCSE Textbook.
You can also get exam questions from your exam board. Personally, I didn't find flashcards and revision guides helpful at all for Maths, but everyone is different.
Don't stress yourself out if you're just in Y9. Right now, I'd say that only a few hours a week of practice (maybe 3?) would be just fine for you. Enjoy Y9, because it's a good year in secondary school (same goes for Y10, except it involves some more work).