It's really easy to get lost in Tokyo which is why I always look up where I'm going on a diddlefinger map before I leave the house. It's great because you can input the address in English and get a map with landmarks in English. To save ink I usually take a shot of the screen on my camera but diddlefinger have just launched their mobile app so you can look up Japanese addresses in English on your phone. The only drawback is that it links to a Japanese map so all station names and landmarks will be in kanji.
Another great tool for finding routes around Tokyo is this website which plots your train route and tells you how long it will take, when the train arrives and how much it will cost.