Today, I would like to introduce a convenient feature of google map when you are traveling by train in Tokyo. If you search your destination on google map in Tokyo, you will get railway routes (train time, fares, time required) to the destination like below. Not just a basic information such as which line to take and what time the train departs from the station but also, the search result will tell you which compartment you should ride so that you can take the shortest way to the destination. As you can see below, when traveling from Roppongi station to Ginza sation on Hibiya line, the compartment that is closest to the exist near your destination is the first (i.e. front) compartment of the train.
Especially in Tokyo, the metro stations are normally very crowded so in order to save your time, it is better to know what is the easiest and fastest way to get to the your destination.