French cyclists are poorer and richer than American ones. They are much richer in cycling skill. You will never see a wrong-way rider, people don't weave about, they ride in a straight line. This is both good and bad for the visiting American. You can learn a lot by riding with and watching these people.
Motorists have different attitudes and expectations than they do here.
As you ride along a main road, you can rely on it that the car waiting at the stop sign at the cross street will yield to you. On the other hand, passing motor vehicles expect you to keep control of your bike and ride in a straight line, so they will pass much closer to you than American drivers would do. When I was living in France I was visited by a good friend who is a noted authority on cycling in traffic and an Effective Cycling instructor. The slight deviaition from line my friend made would have been perfectly safe in the U.S., because cars here assume a bicycle may be ridden by a child or an imbecile, and give a wide berth as they pass. When I was there, helmets were almost unknown.