Reading - make sure you know how your dictionary works and have a solid knowledge of vocabulary so you don’t have to constantly flick through your dictionary. The easiest way to do this is essentially do past papers and see what kind of level of vocabulary is in them.
Listening - similar to reading. It’s important to build your vocabulary up so you can hear key words and at least ‘guess’ if you don’t know the full sentence. You should have a list of all the topics you are covering school, work, weather etc so if you learn vocabulary within those sections you should be fine.
Talking - it’s important to know the correct pronunciation and understand how questions are formatted in case the teachers asks questions about your talk. When I was doing it we basically got given the questions in advance but it’s still important to practice your talk aloud slowly and make sure the pronunciation is on point.
Writing - make sure you understand how french grammar works (this helps with reading too) know your present, past, conditional, future etc and be able to use them with regular verbs (you should have tables of irregular verbs at the back of your dictionary so you probably don’t need to memorise them). Understand the rules for feminine and male nouns as well as plurals as simple things like this can trip you up in an exam setting. Have a few pre learned go to phrases for your writing like paragraph starters ( Additionally, However, On the other hand, Finally, In conclusion etc)
There isn’t really a one size fits all with French it can be quite a tricky subject to study for. But if you understand the grammar well enough to manipulate it and read it correctly and have a broad range of vocabulary you should be fine