Hi Sophia, I'm in the same year as you.
For revision in general, my advice would be to read though your notes and textbooks, but personally I find doing lots of past papers to be the most useful method, especially in Maths and Science subjects, as over time you notice patterns and get used to the style of questions - and in my view, you don't need to understand absolutely everything in the subjects you struggle with: as long as you know what the examiners want, you usually can do well. Obviously this is harder in subjects such as English, which aren't so fact based.
In terms of the specific subjects you mentioned:
Maths: One of my weaker subjects, but I've improved a lot recently by doing past questions instead of simply passively reading through my notes before tests.
Geography: I dropped it at the end of Year 9 as I hated the Physical stuff and found it boring. But from what I can remember from KS3, it's very sciencey based. I looked through some past papers when I was choosing my options and you could probably use past papers a lot to help with revision.
French: I do French and Spanish, and love languages. For Reading and Listening, vocab revision is really the order of the day, but with Writing and Speaking you need a lot of variety, content and a wide range of language. Remember all the tenses (present, preterite, conditional, imperfect, future, immediate future) and you should be OK.
Biology: Again a Science subject, so past papers are the most important (at least in my view).