Going to Japan!!!

I just found out that I am going to Japan for a friend’s wedding!  It’s not for over a year, but I am already excited!  Who has been to Japan?  Where should I go?  I’m finding that in spite of my forays into anime, I know surprisingly little about Japanese tourism.  What should I not miss?  I will chiefly be in Tokyo, but I have every intention of getting out of the city for a few days.