General revision advice
Dedicate enough time to revision
Produce a detailed but flexible revision planner
About three months prior to your final exams you should plan out what subtopics you plan to revise each week (one subtopic would be something like 'enzymes' or 'muscles'). I would suggest two Year 12 and two Year 13 subtopics per week. In the final two weeks (such as during study leave) you should plan what to revise each day. You should aim to cover all topics again but spend more time on the topics you struggle with most. The two days before the exam should be packed full of the topics you really need a refresher on, as well as lots of past papers.
Set yourself an amount of time to revise each day and stick to it. One hour per day in the first 10 weeks, 2-3 hours per day in the final two weeks and 4-5 hours in the last two days is a good guide. But you shouldn't necessarily plan your day minute-by-minute. This is so you can take into account point 3 below.
Be honest but fair with yourself
Honesty: Work out early on what you know and what you don't know. Focus on what you don't know. Use your specification to identify subtopics and exam questions to identify specifics. DON'T be tempted to revise the bits you know well or enjoy the most.
Fairness: If you've tried desperately to revise and nothing's going in then take a break. This is particularly important If you've stuck to your plan on every other day that week as taking time off will likely do you more benefit than harm. The best thing to do is get out of the house/library and meet up with a friend that needs a break as much as you do. Forget about revision for a while. If, on the other hand, you went out with friends yesterday and are out again tonight then you need to get some serious work in now to earn it.
Get some exercise and plenty of sleep
There are numerous scientific studies showing that exercise improves focus and well-being, and will help you sleep better at night. Aim to raise your heart rate for 30 minutes a day, 3-5 days a week. Sleep is necessary to give the brain a rest and prepare you for the next day. Being tired will reduce focus and your capacity to learn. Most teenagers need 8-9 hours sleep a night.
Follow the advice of your teachers
You may or may not have identified yet that your teachers give you useful advice all the time. Verbal comments in class, written comments on classwork and homework, markschemes etc are all useful. Make sure you follow this advice. Sometimes it will be 'big picture', such as "spend some time going back over the light-dependent stage of photosynthesis", while other times it will be specific, such as "use the term 'enzyme-substrate complex' when referring to enzymes". Whatever it might be, follow it.
Don't spend all your revision time making notes
It's always nice to have a perfectly produced set of notes for the entire course but research suggests this is the least effective way to revise. It is very easy to spend an hour writing out notes so you can pat yourself on the back at the end for a job well done. In reality, you will have learn't very little of what you've written because you haven't had to fully engage your brain. You MUST spend more time on (exam) questions and studying the mark schemes than writing notes. After all, if you want some perfectly produced notes why not just buy a revision guide?
Ask for help if you don't understand something
I'm sure your teacher will be willing to help. This is much safer than searching the internet, since your teacher will also know what the examiners will be expecting you to know (and what you don't need to bother with).
Methods of revision
You will see that at no point do I suggest writing notes. After all of the activities below your brain should feel tired, this tells you that you've been working it and, most likely, have improved your memory and understanding.
Use a revision guide
A good revision guide is very important. I like the CGP ones: they're cheap, concise and generally very accurate. Focus on one page (or one double-page-spread) at a time. Read the information. Cover parts up and try to say it out loud or write it down. Check what you know and what you don't and then repeat. Then move on to the next page. An hour or a day later try and remember the information again. Check your answers and repeat.
The best thing to do is make your own questions. This will help improve your understanding when writing them, and your recall ability when answering them in future. You can also find apps with questions (see the 'other useful resources' page), find websites with questions (see the 'other useful resources' page), use the questions in your textbook and revision guide, use questions you completed previously in class, or share questions with friends.
Answer exam questions
This is the only way to improve your analysis, practical understanding, application and evaluation-style questions. Since this will account for ~65% of all questions I would say it's pretty essential. Completing past papers will also get you used to the types of questions you'll face in the exam, and the common mark schemes that go with them. Your teacher should be able to provide you with past papers or you can find them here:
After you've been through the relevant section in your revision guide, you should test yourself on the relevant exam questions. Mark them, pay careful attention to what you did wrong and then repeat. An hour or a day later do it all again.
Draw cycles, diagrams and sequences
Such as the Kreb's cycle, nitrogen cycle, cell cycle, labelled eukaryotic cell, labelled respiratory systems, labelled phloem, stages of mitosis, stages of humoral immunity, stages of speciation, or any other diagrams you come across in the revision guide. Try it from memory and then check and repeat.
Make revision videos
This is one of my favourites. By far the best way to learn is to teach. If you can teach it, you know it. You'll need a phone, tablet, laptop or webcam for this. Simply record yourself teaching a lesson. This could be by aiming the camera at a piece of paper that you draw on, or you in front or a whiteboard, or you could just record the audio. Produce a video on one sub-topic at a time. I would recommend having either the revision guide or a list of keywords in front of you. Keep the videos short (maximum 8 minutes). Get a friend to watch and then you each point out any mistakes or missing parts. Upload the videos to the cloud (I would recommend Google Drive) so you can access them anywhere and on any device. You should find that when you watch the videos back you have vivid memories of making them and, so, a much better knowledge of the information.
Watch revision videos
You can also find videos on-line. There are some good ones but I haven't yet found a perfect set. Here are some examples:
And that's it. If you follow this advice, you'll do just fine.