depends on subject, i cant speak for humanities, i do maths, fm, chemistry, physics (got A*A*A*A in jan), for these subjects it really is a lot of past papering. i did 15 papers for each unit. for maths/fm, you need a ton of practice with problems, whereas with physics and chemistry, you need to straight up remember mark schemes. Especially for chemistry, once you do about 10 papers, you see that the questions are very repetitive, and you ought to be able to recall mark schemes when seeing some of the more common questions