1) USA or HOME-COUNTRY: So, You home-country, mine being the USA, is your life. No matter how much you try to immerse your self in to culture, your habits will be what you do back home! You can try to become as French as possible, but you still will have a few "americanismes." And don't feel bad if people get mad. Like if you speak English once in a while, it IS necessary, I think, to relieve stress. If you speak English for 30 minutes to an hour a day, you will not hurt your French. I usually do, and I still have made a tremendous amount of progress in these short 3 months.
2) YOUR HOST FAMILY: Your host family won't be perfect, so try to work through it. I know WAY too many people have changed host families. Yes, I have thought about it at times, but you need to at least try to make it work. For instance, my family thinks that I am out too much and not home with them....though I am always home. I had some problems with them and they did with me. Instead of immediately telling my family back home and contacting AFS, we had an hour long talk about our problems. Now, everything is much better. Your going to be uncomfortable, but it's normal. Its not your family, so it takes A LOT A LOT of getting use to!
3) FACEBOOK: Try to utilize it as little as possible. I'm saying this cause I learned it the hard way. If you had a great day in France, your feeling very content and not thinking about your life back home, Facebook will pull you right back to America. When you see all of the things that your friends are doing back home, you will get a little home sick. I'm not saying not to go on facebook, but limit it.
4) FRENCH: The French language is extremely hard. So don't get discouraged, especially in school, since your grades will be bad! I'm taking S, the hardest course, and my average is usually like a 6/20. That isn't bad for someone who isn't fluent in French, but that actually isn't that bad for the French neither. So, just keep going and try to speak French as much as you can
Finally: You will make a lot of friends, you'll have a new family, and you'll have the time of your life!!! So, try to be French, but remember IT WILL BE HARD. No lie, being an exchange student is one of the hardest things you can do in your teen-age life. But, it still is an experience of a life time!