Good tips from missmaudie, though I think you'll find that any Visa bank card will be accepted these days. I've been caught out a couple of times for forgetting to punch my train ticket, but the inspectors were generous on both occasions.
So here are five more tips:
1. Avoid the "we do it better back home" mentality. It closes your mind to a fuller enjoyment of the French experience.
2. Similar to the above, but more subtle, is the way upbringing influences public behaviour. It is not rude in France to squeeze past people in restaurants or supermarkets, for example. Don't be too quickly offended by behaviour you're not used to.
3. When you go into a shop or restaurant, it is usual to say, "Bonjour, m'sieurs dames" to everyone in general, or at least to the group of people nearest to you. When you leave a restaurant, it is also usual to say "Au revoir, m'sieurs dames" to the people nearest to you.
4. If you're British or Dutch, don't wear white socks with sandals and shorts in summer! It's a national joke.
5. Be careful of different prices in cafés: coffee is often more expensive if you sit out on the terrace, and cheaper if you drink it at the bar.