Well, the first bit of advice you should keep in mind is that when you are living with your homestay family, you are not there to reproduce your daily routine but with different actors. The rules of the house are going to be different and you will be exposed to a new kind of dynamic. Keep your eyes and ears open, ask permission until you figure everything out (like who takes the first bath? can you sit anywhere at the table? what about chores? who wears the pants (so to speak) how traditional is the family), and be very flexible. You are not a guest - if people are clearing the table after dinner, help. Offer to wash the bathtub or walk the dog. Keep your room clean, learn and respect the house rules. Don't be a burden.
You seem like a smart one, so this is probably obvious, but it is amazing how stubborn and testy we can get when we are very tired all the time and under a good deal of stress (which you will be for about the first month you are in Japan, no matter how much Japanese you speak and how prepared you try to be).
When I was first an exchange student at 17, it seemed my family was quite smothering. I had to be in by 10pm, and had a lot of restrictions what I could do and where I could go. It was not because the were worried I was a bad kid or would do something stupid, but I was sure as heck not given the same amount of freedom my own family had given me. But then I realized my host family was being overly protective because they didn't want anything bad to happen to me. I was someone elses child and if I got hurt etc. they were responsible (in every way concievable), not me. They are supposed to protect me and keep me healthy. They were responsible for someone elses child and that is a huge, huge responsibility in Japan.
Once I got that through my thick head and took it as a compliment and not an insult of my level of responsibility, life was much easier, I enjoyed Japan more, and my host family was put at ease (something you should always seek to do).