if you want A* you have to know everything inside out, meaning you should perhaps work from the specification and use it as a checklist. if you have a textbook you’re reading, make sure it covers all the spec points (if not then you’ll have to research some stuff by yourself) as a lot of textbooks are only at a B grade level.
colourcode all the sections in the spec to see what you need to work on most and start with those first.
allery chemistry is rly good for chem. for bio there’s a lot of processes to remember so you can maybe write down each step of the processes on flashcards and try to put them in order or just memorise it like a story with acronyms and stuff. also for biology, the youtube channel ‘A level biology help’ saved me as she explains things clearly and goes through good exam questions without waffling - it’s good for getting the basics down.
for maths if you want to push yourself you could try solomon papers as they’re meant to be harder so then you’ll find the actual paper easier.