There's more than meets the eye...
This is my second time living with a French host family, and during both of my stays I've noticed quite a few differences from living in the United States. After getting past the culture shock of a new language and moving away from home, there's still a lot to get used to.
One thing that is still hard to remember for me is the bisous greeting on each cheek. Most Americans are used to hugging and the French greeting can feel strange with people you don't know. If these and other cultural norms aren't followed, it's easy to be spotted as a foreigner and sometimes it may come across rude. For instance, when entering a store you must say "bonjour" and "au revoir" when you're leaving. This is the polite thing to do and you can't expect good customer service anywhere without this.
Eating out and meal times
A lot of differences in France have to do with going out to eat and when you eat. Dinner is usually reserved for after 7pm and most restaurants will close after lunch and open again at this time. Don't expect to have the best service either no matter where you go. The waiters will take their time getting to you and you need to save at least an hour or more for meals. They also won't rush you like in the U.S. for the next table, you could spend all evening there and you'll need to call the waiter over for the check or you will be there till closing. Sometimes I do prefer this because you never feel rushed and can take your time. Not to mention the waiters are paid a decent wage so there's no tipping expected either.
A typical French meal includes a starter, the main course, and then yogurt or fruit for dessert. My host family usually has one main course, then we eat the cheese they got from the market that week, and after always a yogurt or fruit. The baguette is definitely an important part of the meal as well. Everyday we get a fresh one from the local boulangerie for dinner. It is eaten with the cheese after the main course or to help clean off your plate. Water at dinner is always kept at the table in a bottle, and served to each person before you take the first drink.
A French breakfast is also very different from an American breakfast. In France they will eat more sweets at breakfast and less meat and eggs. It usually includes yogurt, toasted bread with jam or butter, and sometimes a croissant or pain au chocolat, but that's about it. Coffee with milk is usually had in the morning and espresso's are reserved for later in the day. Although I don't always follow this because I drink latte's at about any time of the day.
Driving in France and French drivers has been something that's hard to get used to. The cars and roads are much smaller, and finding anywhere to park is extremely difficult. No one's afraid to use their horns, and they tend to be very impatient drivers. It's also not uncommon to see cars parked halfway on sidewalks or curbs. I'm just glad they at least drive on the same side of the road as in the U.S.