[jasonbvr]

No shoes or slippers in tatami rooms.
Close the door to the bathroom when you come out.
Shower standing outside the tub, and shower before taking a bath.
Itadakimasu before a meal. Don't start eating before everyone else unless they say, Osaki ni itadakimasu. After you eat, they say something but I forget what it is.
Tadaima when you come back home, shitsureishimasu when you are going out for the day, and ii tekimasu when going out for a little while. The responses to these I forget.
In general, say oneigaishimasu (a mix of like please and let's do it, real meaning doesn't translate), sumimasen (excuse me), gomen nasai (I'm sorry) and arigatou gozaimashita like every ten minutes. When and which ones to use you will learn by watching the others, but seriously 90 percent of the time Japanese are speaking one of these words/phrases will be used.
Oishi-delicious
Oishikatta-it was delicious
Ona kaipai-I'm full, I use this to politely refuse them trying to turn me into a fat cow by feeding me too much. Not that I have a host family feeding me, but I do have an adopted Japanese family and grandpa. And for some reason Japanese guys really like to get me drunk and be buddy, buddy with me.
Tanoshi sou-sounds fun, for when they want to take you somewhere.

And that is all I have. Oh wait, don't forget your omiagi when you come from home. I would bring skittles and jolly ranchers. Just basically any food that they don't have here would work. Definitely bring some Skittles and then mail them to me. The plain ones, none of that funky tropical fruit stuff. Sour would be fine, but I don't think they come in five pound bags.