Tokyo is a walking city only within particular neighborhoods. The subway system is a far better choice than the obscenely overpriced taxis, and a lot faster.

Contrary to popular belief, subways are fairly easy to use, although it may take some time to cover the distances from one area to another.  Majority of stations have an English language ticket dispenser.  All station stops are also in English, and even on the trains there are signs and announcements in English. Changing trains in a station is not complicated, but can be time consuming, as the big stations are, well, big. One important piece of advice - try not to take the subway during rush hour. It’s not a pleasant experience at all.

 That being said, it's definitely advisable to plan your journey and know which JR or subway line you have to change to. It makes the journey much easier. The directional signs are clear and they have English directions. Once you know the line which you have to transfer to, it's not difficult finding your way around at all.

As an aside, the major stations have pretty good and not too expensive restaurants.

Journey and fare planner: (in English)

Here is a link to information about: Getting Around Tokyo