I finished my Alevels this year and got A*AA in bio, chem and maths. I struggled to revise effectively in yr12 but ended up finding some revision methods that worked for me, even though some motivation and mental health issues kind of killed my vibe when it came to revision in yr13. The first thing I would say is that often, each subject requires a slightly different revision method. For example a science and essay subject may not be revised effectively in the same way.
Personally, in the sciences, condensing a chapter each onto one 6x4” record card was incredibly helpful. Making them using the specification is also key so that you actually have the relevant and useful information (especially if you use the kerboodle textbooks because they waffle so hard). For chem I also made a manual for organic chemistry that outlines the reagents, conditions and mechanisms for each type of reaction in the spec (e.g. elecrophilic substitution/addition, etc) as well as organic synthesis pathways. For bio I found making diagrams, flow charts and drawings on the record cards actually also helped. Especially for visuallising things like the cardiac cycle/initiation and control and the nitrogen cycle.
I also took History in yr12 but dropped it at the end of the year without taking an AS as my school didn’t offer it. For that my friends and I found timelines, mindmaps and small date flashcards useful for linking and memorising information. For essay subjects i would also prioritise essay plans and practice essays (both open and closed book) as those are INCREDIBLY useful for both revising content and structuring your arguments. Make sure you keep them and have your tecahers mark them as well.
My school forced us to take notes for textbook chapters but I found that to be less effective for me as a single revision technique as it tends to become monotonous and I would zone out frequently. To be fair, they were mildly useful in then going on to create the flashcards but i would often end up looking at notes online and going back to the textbook anyways.
Also just PRACTICE AND PAST PAPER QUESTIONS. If you cant be asked to revise one day, at least do a couple of those. They are literally the best thing you can do. Get a study buddy! Or revise with your friends! Especially before exams. My friends and I did that before each of our papers and during study leave and it was so helpful, quiz each other, mark each others papers, draw diagrams on the board, explain topics to each other, etc.
Despite all that yapping, I’m probably missing some stuff. However, out of everything, make sure to make a routine out of revision. Study a little less more frequently so that you don’t get overwhelmed and don’t cram during exam season, make flashcards/info cards and do questions/essays on chapters as you go through them in class. Also don’t start grinding at the beginning of yr12 and then get burnt out like I did because I got so tired of revision that I actually maybe did like 20hrs total revision in the whole of yr13. It was bad. Don’t do that.