Past papers. Past papers. Past papers. They can't be over-emphasized. When it comes to A Levels, learning the structure of questions and the marking techniques makes a massive difference. Practice as many question papers as you can. As you get closer to your exams, practice those questions under timed conditions. Do make sure to start with topic-specific past questions before moving onto general past papers because you won't know everything in Year 12.
Notes. If note-taking helps you learn and makes revising easier, please, stay on top of it. Try your best to not fall behind and ensure your notes are organised and up-to-date at the end of every week. That feeling of being only a few weeks from the exams and not having compiled notes to revise is awful.
YT videos. With all the information available online and free lesson videos, it'll be a crime to not take advantage of such resources. If there's any topic your teacher isn't explaining well or any one you're stuck on, just search for it there and a ton of free lessons will show up. Videos like that saved me numerous times.
Topic list. A few weeks into Year 12, you'll be able to notice which topics you struggle with and which ones you're good at. Place them in different categories, write them down and paste them on your wall. Allocate more revision time to the ones you struggle with. Putting more energy into the problem areas makes studying more effective.