Maths - AS is quite easy, so it wasn't the case that I did every question from every chapter. We did the easy stuff in class, and I'd do the last few questions as exercises to make certain I was confident with it all. The youtube guy was super good at clearing up any uncertainties. Just be confident with basic techniques, cos they like manipulation, and even more so at A2.
Chem (ocr b salters) - it actually took a good deal of getting used to, but I made notes from every textbook chapter, including some A2 chapters (albeit much later than I should have) and it all came together. Mark schemes are quite important
Bio (edexcel) - the content overall's pretty good, with human bio being the most interesting. I found that working fairly constantly with bio really helped - I ended up making a disgusting amount of notes, and drained myself out, actually. The textbook had loads of context crap, and so I often looked to other sources.
Physics - unit 1's not actually that bad, but go by everything you're taught (my physics notes were the best) because teachers probably have more materials than you would ever have access too. The spec is really dodgy I find, so do this. The textbook is decent, it think, but there are loads of mistake, and a fair bit of waffle. For unit 2, learn mechanics by yourself - and not within the narrow confines of the spec, or what you've been taught - because then you could answer anything, really. When I sat my unit 2, there was a moments question that I think even further mathematicians (who do M1 and M2) couldn't all do, or at least struggled with. I went home thinking I had gotten wrong, since I guessed it, but I was right, and they were wrong aahahahahaha. Learn markscheme answers for fibre optics (wasn't in my exam though
)
Obviously doing all exam papers is a must, I found.
I was not confident collecting my results, but I got >90%, so something must've worked