Memorise phrases/sentence starters that allow you to easily incorporate harder grammar into your writing/speaking and make sure you're really really confident on grammar in general so you don't lose marks over mistakes that you wouldn't normally do if you weren't under exam conditions. Whenever you watch tv/a movie, add french subtitles or watch the french dub with english subtitles (or watch french tv/movies). Practice practice practice. Do loads as many papers as you can and talk to yourself in french when you get bored.