Getting lost in Tokyo is part of the experience.

As others have pointed out, there are plenty of maps in street corners and they are very useful after you realize that typically up means direction where your nose points when looking at the map rather than north. Also locals are usually very helpful but often there is a considerable language barrier. Subway and train stations are usually quite good reference points. Subway map that has English names in one side and Japanese in other side is very useful if you are totally lost and no one seems to speak English. Just point a Japanese name of a station you think is nearby and the person helping you can at least point a direction to go. It also helps in inside bigger stations if you don't find a correct platform as you can point where you want to go.

Smartphone with map is naturally helpful but one can survive without. Just reserve some extra time for getting at least little bit lost once in a while and take it as an experience.