Take a walk on the nearly wild side
One of the many characteristics of Japanese people is their large tolerance for fashion.
Aoyama district is the fashionable place to be for all fashion victims "with classe". Aoyama street is the place to be for fashion designers of the world. They show off their season collections in really nice looking building, designed by architects with a wild spirit. Prada building is my favorite but really, you will find the esoteric and, yes a bit posh, cafe of Comme des Garçons quite refreshing, with a beautiful vegetation wall (Minami Aoyama 5-2-1)
A new development is the transformation of a NYK company restaurant into a very fancy place with a South of France cuisine restaurant called Cicada (minami aoyama 5-8-28) http://tabelog.com/tokyo/A1306/A130602/13004580/
So, you will find there a very gentrified public, civil and polite and polished.
But if you, and you should, venture in the small streets, you will find a different public, mixed and with a very open spirit towards fashion. If you choose to sit around and watch people, time will fly. Gothic Pierrot and neo-punks are walking next to chanelers... you will find yourself translated into the Mars reception of the 5th Element...
Close to Omotesando station, next to the Franc Franc shop, you will find a large square invaded small temporary shops, and a huge terrace. There, you may have something to eat, to drink (beers and mohito available at all time of day and night), to make a pause, enjoy the music.
If you prefer a more quite place, I recommend "Nid de café", a small café on the third floor, in the next building. Downstairs, there is a flower shop.
So, discovering Tokyo, is not only about traditional sites but also about meeting the people who are making it alive!