I'm a current 3rd year astrophysics and cosmology student and have plenty of experience trying to do better in physics, especially during a-levels. A main thing I suggest doing (sooner rather than later) is going through the topics that are going to be assessed and see where your doubts are. This is where you should focus on and if you need help, ask your teachers about that tpic and get anything clarified so you fully understand that concept.
Next, start doing practice questions but open book so you practice how to go from knowledge to formulating the answer to questions. This can be quite tricky to get a grasp of, especially trying ti understand what some questions are actually asking for.
Then finally, do as many practice papers / questions as possible! I highly recommend using the "physics and maths tutor" website for revision as they have so many questions, filteres by topics and full exam papers when you feel confident enough to do those. They also have revision resources like flashcars and summaries, but these do not go into the full detail you need to answer questions sometimes. I also recommend "science shorts", they have videos and mindmaps of topics and do run-throughs of questions too, so definitley check those out, as they helped me during my a-levels too.
I hope all this helps and if you have anymore questions, feel free to ask!
Good luck with the revision!
-- Arya (Lancaster University Student Ambassador)