I got full marks for 3 out of 4 of my subjects at A2 Level - the other was a B in English, the exam being taken the day after my mum was hospitalised with a stroke and quite honestly I'm impressed with a B. I feel my revision was the key.
I used revision cards, mind maps, and MASSIVE theory sheets. I can't find my USB otherwise I'd upload a picture. But often I would stick 4 or 5 sheets of paper together, each with different topics on using LOTS of colour, and stick it on walls. The paper would be stuck together so to lead on from the previous subject well (linking topics or something).
Mind maps work really well for thematic work, which was especially key for my history exam, which involved looking at a whole period and analysing continuities and change. So I would do a mind map for the progress (or not) of peasants, and short evaluative sentences to show why they did/didn't change.
Annotating books worked well for English, with sticky notes and stuff like that. I reread the books a few times, memorised a few key quotes and themes, but like I said, that didn't go so well due to my situation at the time.
I strongly, strongly advise revising your arse off for AS and A2 - it'll pay no end at degree standard. The amount of people I've met at Uni who scraped by with, say, BBC or something with little revision are completely dumbfounded by revision at degree standard.
To me, it is time; I can revise (and usually do) all day, with very few breaks. It helps me cement my thought, and I give 2 or 3 hours to each topic.