I do think an important thing to note is to not just work through the specifications chronologically - go over the harder bits first and then go over the easier bits if you have time. And always focus on exam technique.
For chemistry, I don't think making notes is the best/most efficient way (for biology it could be useful if note-taking helps you remember things). I got A* and I took a mostly exam based approach.
First off, I printed out the specification and marked the topics red/amber/green depending on how much I struggled on the topics or how easy they were. I went over the red topics (notes/textbooks, videos, talking to classmates/teachers) until they got to amber/green. Then I moved onto this, which is probably why I did so well:
1. Timed practice exam paper, mark using the mark scheme
2. Identify the topics I did badly on
3. Make sure I understand why I went wrong (mark scheme, videos)
4. Exam style Qs based off these topics, mark using mark scheme
5. Repeat
This method allowed me to practice exam technique and application of knowledge/skills, while guiding me in my revision to master each topic in the most efficient way possible.
For biology, I printed out the specification and made flashcards for each bullet point (I did start doing this from the very beginning of the course though so I'm not sure if you're gonna have enough time for this), including some good exam Qs. I also used the exam0based approach I described above. Another useful method is the brain fart method:
1. Pick a topic and write down everything you can remember about it.
2. Read through the specification and your notes. Then use a different colour to add to you brain fart AFTER reading your notes but without actually reading them while you add stuff (if that makes sense haha)
2. Then use a 3rd colour and add to your brain fart WHILE actively using your notes and the specification.
I hope this is helpful
Good luck!!