I was also a bit nervous getting ready for an exchange student but it was really fun. He was 15 and came from France but for only 3 weeks. He was such a nice kid and our 3 boys had a lot of fun with him as did my hubby and me. One thing I'll never forget is how shocked he was that we eat snacks watching movies!! We sent him back with baseball stuff as he loved baseball. Two of our sons studied abroad in college and the experiences were wonderful!!
Oh- as for advice- don't worry about anything. They want the American experience!! :D