Structuring an essay can be a very subjective thing, there are always a few basic rules to remember - especially when you're under the time pressures of an exam!
Introduction - This is where you address the question and give context of the novel/film/other cultural work you have studied. Perhaps outline the key characters/themes, depending on what the question is asking of course, and don't forget to outline the structure of the rest of your essay.
The main body - This should be around 2-4 paragraphs, and each paragraph should contain a different argument/theme/character, question-depending. For instance, if your question was "Dans le roman que vous avez étudié, comment les personnages féminins se développent ?", you would take three or four key female characters and analyse their development, perhaps stating which you think has the greatest development throughout the novel and which you think shows the least development.
The conclusion - Your conclusion will allow you to consolidate the arguments you have made in the main body of your essay. This should be no more than five or six sentences, and do not be tempted to add new content into your conclusion!
Maintaining a consistent structure throughout the essay will ensure that the examiner understands exactly what you are trying to say, and increase your mark for coherence!