Hi, I study French at university, and got a 9 at GCSE.
I'd advise you create a list of possible questions related to each topic. Have a think about what you'll include in your responses.
Then, get a family member/a close friend to ask you them in a random order. You should do it fairly regularly. Each time, you'll get better at structuring your answers and begin to feel more confident having a discussion. Memorise complex grammatical structures and how to use them, for example, 'si clauses'. Include a variety of tenses (passé composé, futur proche, conditionnel, etc). This should hopefully allow you to access the higher marks.
A wide range of vocabulary always helps. Usually, lists will be provided by your teacher. If not, check the exam board website. If you have already created resources to revise vocab, it's just a matter of keeping up with it and engaging with the material regularly to keep it in your mind.
Don't forget you gain marks for pronunciation and intonation. When you speak, don't rush. Your responses should have 'natural pauses' in them. If you struggle with your pronunciation, listening to native French speakers talk and then repeating it back is probably one of the best methods you can use. There are many YouTube channels with resources for this.
If your teacher has advised you to prepare and memorise responses to any questions, just keep reading them aloud and testing yourself on them.
If you have any other questions, feel free to PM me.