Tokyo stations can be confusing to navigate. When you get off the train, take a few minutes to read the yellow signs and maps (found on the wall facing the trains, on pillars and from the ceilings), indicating which exit is most suitable to you.
The journey to each station is also indicated...
Even better, you can find out where are situated the exits/stairs/elevators for each station on the train/metro line you are using. Thus, saving time and hassle when you get off....
