It is important to remember that the examiner has thousands of essays to mark, so you want to make sure yours ticks all the boxes while still being interesting. Firstly, it is important to nail your grammar and vocabulary - create a checklist of impressive grammar points (such as a variety of tenses, the present participle, the subjunctive mood, etc.) and a list of phrases you like and will remember. Secondly, it is also important to remember you can take some form of creative license (as long as it is not too extravagant). If the essay topic is about family and all students take the approach of 'J'ai deux frères et ma mère est actrice...' your essay will simply blend in! However, you could tell an anecdote from a family holiday or perhaps a childhood memory, as this will give your essay an edge compared to others. Finally, you have to enjoy what you are writing (as difficult as this may sound), you can always tell when someone genuinely believes in their work, and this makes a complete difference for the reader.