I'm visiting Japan (Tokyo) for the first time soon!

I know very little about visiting Japan. I'm trying to absorb some quick advice from websites, but is there anything I should prepare in advance? What do you wish you'd known?

@saraislet Do *not* take a taxi in from Narita (if you can arrive at Haneda that's better but usually you can't). Take either the Narita Expresss (N'Ex) or the Keisei highlander. Faster, and the taxis are insanely overpriced.
@timbray @saraislet NEx has some reserved seats as well as non-reserved tickets. I didn’t realize this and had to move, which was confusing with a language barrier.