What part? Tokyo? Roppongi is probably the easiest place to have a night out since it's full of whites, which frankly can be a relief after full immersion.
A pretty interesting place indeed, would love to go back some day. Definitely a weird feeling being white, and a minority there. Lots of really nice people... a very respectful culture. But... in the same breath, you don't have to spend much time there to experience racism. For a white person, that just doesn't happen in North America.
QFT. On the upside (depending on your point of view), I found it to be a very male oriented culture in my short time there. If you're with a woman you will be treated as the one who is more important, which might piss off a western woman.
Just be easy going and keep a friendly look on your face, since they might mistake a look of confusion for displeasure, especially if you're a big dude. If you are going alone, you'll probably find two extremes when meeting the Japs - the one's who are very friendly, curious about you, keen to talk, and easy to meet with nothing more than a 'hello,' and the opposite extreme - the ones who have zero intertest in breathing the same air as a gaikoku and make it obvious.
Make an effort to learn some basic language skills before you go since it will cast you in a good light. Also, Japan is one of the most interesting places in the world imo from a cultural standpoint but you need to be able to understand what you're looking at. It's not obvious or accessable to the uninformed westerner. Read up on Japanese notions of beauty. Garden architecture is a good place to start. I know that sounds weird but the uniquely Japanese arts, like Jap garden design or poetry, will show you threads of thought that run through Japanese history and society and which you will see over and over if you know what you're looking at. Learn some history and get an idea of the significance of places you're planning to visit, as well as the origin and significance of popular Japanese activities like theatre or sumo, or even baseball. It would be a shame to go all that way and not understand what you're seeing.
Obviously, get educated on social gaffes to avoid such as not taking off your shoes when required (have shoes that are easily removed and replaced btw) or eating in public, but it's not as complicated as most whites make it out to be.
