I sent the following message to someone last week as they asked about how to get a decent grade in AQA Biology. I did more or less exactly the same for AQA Chemistry so it is relevant for that too. Not going to edit it but might help someone.
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I basically did 2 years of A levels first, getting a D at AS then an E overall. I then went to a college and retook the whole A Level in 1 year, so the AS exams were done in January and the A2 exams in June. The 2nd time round I managed an A*.
Firstly you need to make sure you have the Nelson Thornes text book. I assume you already do, but it's certainly very good. It is worth noting that I was lucky in that at my retake college the teachers were VERY good and covered the syllabus comprehensively.. so I was able to produce my own good notes. To aid revision I also bought the Philip Allan Updates 'Student Unit Guides' - they produce one for each unit, so 4 overall. These revision books do not cover absolutely everything and have some stuff in them that you don't need to know.. but some of the diagrams are excellent.
When it came to revision the first time, I simply tried to revise by reading a revision guide and I spent very little time doing that. It was obviously completely the wrong way to go about revising - I was going into the exams with a few topics learnt very well and simply hoping that they would come up in the exam. More often than not they didn't.. so I flopped it.
For my AS exams in my retake year, I was revising for them at Christmas. My revision method was fairly simple.. I used my notes, the text book and the revision books and produced revision cards. These were basically A5 size pieces of coloured card and I wrote on both sides (I cut lots of A4 pieces in half). My aim was to use the information from all 3 sources to produce comprehensive revision cards with absolutely all the information on them, but as brief as possible.. so none of the waffle. I would say I spent 4 to 6 days working 8 or 9 hours a day over Christmas doing this for AS.
Then, a bit closer to the exam, you can just go through all of your revision cards and make sure you're happy with everything. I did exactly the same for A2.
It's also important to note that during term time I had been set past exam questions on the topic we had be learning every week. So I was getting used to what type of answers are expected to get the marks very early on. For revision you should probably go through all of the past papers (there aren't that many because the syllabus is fairly new) and use your revision cards to answer the questions as well as possible. Then use the mark scheme to go through and see where you missed out points. You can add to the cards if you need to.
This method works mainly because by reading your notes/textbook etc and rewriting the information into revision cards, you learn an incredible amount without realising. You then have all the information in a really concise form so it's very easy to read over them at any point before the exam and touch up on your knowledge.
It basically got me 100/100 in Unit 1, 140/140 in Unit 2, 100/100 in Unit 4 and 128/140 in Unit 5.
Hope this helps.. good luck.