1) I am American, but don’t have the Japanese image of a typical american. According to Japanese people I am skinny and small (I weigh 118 and am 5 ft. 4 1/2 in.) which they found surprising as there is an image of americans eating McDonalds frequently and being fat. Don’t be offended.
2.) If female- wear a hat when going out in the sun. In the city its not such a big deal, but in the more rual areas there some form of understanding that darker skin is not good. Possibly, I do mean possibly, there is a historical association been farming women and noble women or non-working class women. In Japan being pale is good.
3.) No matter the gender take care with appearence, it means a lot．Women wear makeup and keep complextion clear.
4.) Bathing is important, do it at least every other day if not every day. However if at a homestay wait until you are invited to take the bath, there’s something along the lines of a hierarchal order. My current siuation is Father, Mother, then me unless invited to go before.
5.) Watch. Sounds strange but take time to watch and observe, a lot of things are done quietly in Japan, so sometimes the best way to learn is by watching and copying. Or by watching and later asking questions about whatever.