I often get asked how people dress in Japan and I usually reply that it depends on the city. I grew up in Narita City (a fairly quiet suburb) where the style is more often than not on the conservative side. Many women in Japan refrain from wearing clothes that reveal a lot of skin, in particular, cleavage. Which means deep v-neck shirts are pretty much nonexistent. However, in Tokyo, the dress code is very alternative.
Remember Gwen Stefani's Harajuku girls? Well, Harajuku girls don't really exist, but you can see a bunch of other types of unique fashion in Harajuku. No matter how crazy your look may be it's really not that big of a deal in this big city. Actually that's not entirely true, you may get some stares but nothing that is threatening. To get an idea of some of the subculture fashion in Japan, this article, "20 Tokyo Subculture Fashions Explained," gives you a simple breakdown.
On my trip to Tokyo, I wore clothes that were easy to pack and also something I would wear in the states. I didn't even bother packing a pair of heels and wore my converse the entire trip. There is a LOT of walking and tons of stairs. There are plenty of escalators, but when they are not available it's no fun if you have those heels on.
I would say a good rule of thumb for Japan is to dress conservative, unless you are in a big city like Tokyo or Osaka, if you don't want to get stared at.