The most useful signs in the train station are these - they tell you which carriage to get on depending on the exit you want at your destination.
So lets say I am at Shibuya and want to get off at Meguro - I can see that the exit at Meguro is by the 11th carriage. I get on the 11th carriage at Shibuya so that I arrive right in front of the exit when the train reaches Meguro.
