I just use past papers. No other method works, for me anyway.
I do a past paper a week for each of my subject, so four. Plus, I go over the paper I did the last week, by checking the markscheme and watching videos/looking at solutions.
It takes roughly 10-15 hours a week, I also watch videos/read outside my subjects + do hw. After feb I'll start to do more, but some subjects there aren't enough papers so I'll just do questions etc.
Maths there's an abundant amount of papers, as you can use basically any exam board (there will be small variation, but the ones you haven't learnt you can skip).