start your revision early so you don't cram (coming from a person that didn't) its way less stressful, you have more time.
Don't revise from September. What I think you should do is try and learn from the back of the specification or ur revision guide especially for science because the teachers always rush by the last few topics and they are the hardest e.g electromagnets in physics I found really hard and the end topics in chemistry. Once you've learnt all the content start ur revision bit by bit. Try making good habits. For me I found whenever I went on my laptop I would get so distracted do what suits you and what you've already been doing all year round.
Keep your same revision methods if it has worked for you and if it hasn't then maybe switch them up a bit. Also don't worry u won't forget but make sure u keep actively recalling what u have revised using different techniques e.g past papers, flashcard questions, quizlet has good ones, videos (freesciencelessons for science was a lifesaver), etc
I do bio, chem, psychology a levels. Chemistry is basically the same as gcse if you love it at gcse then you will be fine it is just a bit harder and more detailed there isn't much content and once you have learned it all you need is practice. Biology is way more detailed than gcse there is so much content everything is in such fine detail and you have to know it all, depends on the exam board (but so far I get higher grades in bio weird?). Psychology is way different than what I expected I thought it would be more interesting which it is but yeah. It is a lot of content and memory but the content itself is easy just remembering is hard because you've got to remember A01, A02 and A03. (I've just finished AS level idk abt y13 but up to now its good)
good luckkk<333