As a U.S.-based (female) I have many many times had interviews for jobs either with a French entity based in the U.S. or in France. Knowing as much and as little as I do about French culture, I know that rules pertaining to questions permissible during an interview in France are vastly different from thaose in the U.S.
I relay this information without judgment, just as a mere caution and useful information.
1. French resumes all include a picture, age, nationality, and marital status as required items and this is also situated on the resume next to the name and address and is therefore amongst the first informations that a potential employer will see.
If you, as an U.S. citizen, do not place this information on your resume - be prepared and expect to be asked. This is fair play. (It is illegal however to ask about religion).
Drawing from own experience, I have been asked in interviews about my age, my plans to have children, and my current relationship status (even to the extent of being told "great!" when I said I was newly single). When interviewing in France, I am "expected" to answer this; in the U.S. but interviewing with a French entity, I see it as up to me if I want to respond. This may or may not happen to you - as after these experiences, I relayed the story to French friends who were shocked and horrified at the indiscretion.
2. The more you know about France, the better - really. The stereotype that all people from the U.S. know about France is Paris and the Riviera is still somewhat rampant and the more you can disprove this with your knowledge of other cities, of Frnech history, culture, language - the more you will endear yourself to them and therefore to the job you are seeking.
3. Language is taken seriously; so is formality; and so is protocol. Use the vous until you are told not to; default to the proper and formal - always.
4. The French work environment may feel more pessimistic as compared with that in the U.S. (if this is what you are used to) - but look deeper, its not its just a different way of loooking at work. The French are "born" with certain rights in terms of work contracts and they dont see it as it is seen here in the U.S. (as in its a privilege to have a job, paid vacations, health care.... these are rights in France).
5. The French make about half of salaries for comparable jobs as here in the U.S. - know this and be cautious when negotiating salary. They did not pay $60,000 for their studies nor do they pay for health care with high premiums as we do - also they are guaranteed at least five weeks paid holiday. Normally, you also have on RTT per month (day off) and your lunch is paid for through tickets repas on days when you work. These added benefits add up. The French also have a better work/life balance and vacation is to be taken, not paid out.