My top tips would be to use websites such as quizlet.co.uk in order to boost your vocabulary and if possible to watch French films, read French books and talk to your friend in French. Remember that I'm no expert but this might help you.
En ce qui concerne (Concerning) is one sentence starter that might help in an essay. Tout compte fait (Everything considered) is a good way to finish.
To improve your essays I would agree that practice is important - what I'm actually doing right now for my french A-level!! In all, just do your best and good luck!!