I've just finished my French A Level and loved it.
4 basic tips I would give are:
- Use impersonal expressions - in particular 'il s'agit de' and 'il faut' - In doing so you sound more French and 'il faut' can be turned into a subjunctive by making it 'il faut que'
- Don't obfuscate - from what I've seen and read, the best French is simple, and too many people when asked to write a response simply look for posh sounding expressions (my least favourite being 'la premiere constatation qui s'impose', etc.) because they believe it enhances the quality of their work - it doesn't and makes it sound too over the top and un-french. Moreover, try to not go overboard with the subjunctive. If used too often it makes you sound pompous. I basically limited myself to 'bien que', 'pour que' and 'il faut que'
- Read! Definitely read articles and try and get as much vocab as possible from them. Read books too if you like, but I found them either too long or too archaic for me to effectively revise vocab from them.
- Using participles - One thing I've noticed is that the French LOVE past participles which they use to 'strengthen' (I can't think of a better term) their nouns. For example you could say 'les decisions de la Cour Supreme' although I would prefer to say 'Les decisions PRISES PAR la Cour Supreme'. Both sentences work, but using participles in this way will gain you grammar points and also sounds more French.
Best of luck and feel free to ask any questions!