>>72375While I'm sure there are urban Japanese youth that don't give a crap, what's been said in this thread mostly agrees with what I saw when I was an exchange student in Japan, and with how the Japanese exchange students at my uni behave. Of course, Japanese are good at hiding what they think so if you go around behaving like a self-centered prick, you probably won't even notice that your stay in Japan wasn't appreciated by anyone else than you, and you certainly can get away with almost anything just because you're a gaijin. I think this advice is mostly in the case you want to make the effort to fit in.
I would add, though, to what's been said that don't overdo the politeness or dressing nicely thing: being neat and respectful of older people is sufficient.
Be open and friendly, but for gods sake DON'T FORCE EVERYBODY'S ATTENTION ON YOU ALL THE TIME in a conversation. This is the biggest fail for many Americans in Japan. Learn to shut up and listen, don't turn every topic into an anecdote about yourself. If the discussion is about you, then fine, speak about yourself. But if it's about somebody else, make it stay that way, even if somebody asks you if you've had similar experiences, don't steal the attention.
If you notice some of this doesn't seem to apply in your "in-group" in Japan, by all means adapt to your group's own norms. Rather, use this advice as a general guideline to follow until you know better.