hey! i got a 9 in gcse and i'm currently predicted an A for A levels (honestly a shocker). some tips i found useful was having a separate notebook for new vocabulary. keep revising grammar topics, make sure you can do it in your sleep. it will become so helpful later. make sure you are reading articles from french magazines (phosphore releases i think a monthly e-magazine). work your way through the articles and try and translate them. try and speak to someone in french for like 10 mins a day. i found music really helpful especially because there is a music topic in the syllabus. keep up to date with french news and culture, it helps with the speaking exam.
The jump from GCSE to A level can be massive for some people but just stay on top of your work and you should be fine. don't forget ur gcse work because it all adds up in the end, build a good rapport with your french group because it's always nice to have people who are probably struggling with the same things you are struggling with, you can end up creating a good support network. have fun and don't lose interest in it because then it becomes tedious.