I'm pretty sure you'll love it. In general, Japanese people like foreign people and try so hard to communicate. It's like you don't need to do much while you're there, especially if you're around the tourist-populated areas. The problem is that most people don't speak English, so knowing the language would definitely come in handy when you're walking around alone. But when in doubt, there's likely to be another tourist or English native speaker near-by, so don't be too affraid to ask.
Personally, if you were going to do some sight-seeing, I'd recommend places like Odaiba. They have a TV station there (Channel 8 Fuji TV) with the most funny looking architecture of a building. Great for shopping, and if you're Japanese celebrity savvy, you might see some. You can actually see inside the studio, and if you're lucky, they'll be shooting for a TV show. But other than that of course, the view is absolutely perfect. From Odaiba, you can see the rest of Tokyo. Beyond the Rainbow Bridge, you see Can see
Tokyo Tower accross the bay. Go there during night or day.
If you want to go shopping on the other hand, Shibuya and Harajuku are some nice places. Just wander off somewhere, walk around. Just remember which direction you came from. If you get lost, there's always a train staition near by in Tokyo (subways or ground level, they're everywhere), and they'll likely have maps to show you where you're at. Other shopping area's would include Shinjuku, or around Tokyo Dome (which also has an amusement park) in Suidobashi. Ueno and Akihabara aren't bad either.
The city of Tokyo is a pretty dense place, so you're bound to find something anywhere you go. Walking is pretty much the only way around, and the place is just SO crowded on weekdays, so just beware of that in some places and when you're making plans.
For more quieter places, get out of the city.