Draft an outline for your story but keep it simple. Write only in French using your English/French dictionary and grammar reference to help with vocabulary and sentence structure. Do not be tempted to write in English then translate into French. Your story outline should include details of your main characters (including what they look like, how they behave and how they speak), the plot and conflicts, the main scenes, ideas for imagery, the mood of the story (sombre, happy, scary) and some ideas for dialogue. If you have been given a particular assignment by a college professor or language tutor then you must make sure your outline addresses all the requirements of that assignment.
Write your story as you would in English. Tutors at Vanderbilt University recommend you put away your grammar book and dictionary when writing until after you have completed your first draft. Try always to think in French as you write, rather than thinking first in English then translating. French sentence structures are quite different from English.
When you have finished your first draft, check your punctuation and spelling and then look at your sentence structures and verb use. Correct any mistakes and check again and again, as advised by tutors at Pomona College in Claremont, California. You will need to pay particular attention to the various accents used in the French language. Note if you have used repetitive phrases; use your thesaurus to find alternatives. If possible, ask for feedback from a more fluent or native French speaker on your draft. Make any final corrections, et voila!