I was an assistant many years ago - I applied for , and got, Toulouse. Great city! I'd suggest he thinks in advance about how he'd approach coping with the different environments of a city and a small town, and be ready to give a few strong reasons for his preference. He might need to be ready to respond to questions about teaching in primaries as well as secondaries. Both are an opportunity to get over that he has some ideas and creativity about how to teach. Good luck!
If he hasn't already done so, he may find this useful:
http://www.britishcouncil.org/languageassistants-tutors-france-countrynotes11-12.pdf to show that he knows what to expect.
He could also have a look at their teaching website: http://www.teachingenglish.org.uk/ for some ideas, and I would assume if he is already taking a TEFL course he has some awareness of methodology, language etc and can demonstrate this in interview.
He will be teaching English. He is thinking of a career in teaching and this should help him decide. He thought he might go for the easy option of Spain as we lived there but he realised that he wouldn't get anything out of it and because of his level of Spanish the Uni have agreed that he won't have to split his time. Ellen was a bit worried about the application process as they turned down about a fifth of applicants last year as less places are available due to the education cuts in many EU countries and here this option is becoming more popular due to the pay. He doesn't want Paris but knowing the BC that might be what he gets! He is a confident lad who is doing a TEFL as part of his degree so he should be ok. Only down is that because he was educated outside UK he is likely to be interviewed by phone - which he will hate. Anyway the Uni appear to be on the ball with this so far - let's hope it stays that way as I've heard many places are dire.
I have loads of friends who've done this and I'm trying to pick up a vacant assistantship in a local high school (the assistant didn't turn up!), but not via the BC scheme.
Requesting somewhere random is better than, say, Paris. Everyone wants to go to Paris but people rarely want to go to the north east of France.
Talk about experience of dealing with adolescents. Some schools are pretty tough and they want to know that people will cope.
Stress both his knowledge of French and his knowledge of English - sounds obvious but many people forget that you're there to help with English, so being able to explain the rules/demonstrate pronunciation clearly helps!
I did a year as a British Council assistant, half on the normal scheme and half on comenius. I had to interview for one of the posts but not the other. The applications are straight forward from what I can remember. I know loads of people who have done this and don't think I've ever heard of anyone being rejected so he shouldn't worry about the application. He should just make sure he comes across as a well rounded, confident person. Also he should definitely be aware that people often end up sent to some random place which is not exactly the location they chose, so he should be open minded and ready to make the most of it wherever he is. I was in Belgium rather than France for my French speaking part of the year. I'm sure there will be a few talks or sessions on it for students in his department to help them find out more about it and help them with their applications.