The Métro de Paris is an easy system to navigate, and with a few simple instructions, color-coded lines, one can cross Paris with ease.  The maps are consistent in the color assigned each of the 16 lines, and the Métro stations themselves are well-marked with signs so you will arrive at the proper platform (headed in the correct direction).   Before you leave a station, a map on the wall will show you the exit(s) and where you will be at street level.  I have found that a compass or an iPhone app with a compass is helpful as you come up to the street in an unfamiliar area.  

The photo above was taken for the chic attire of this Métro passenger, but it reminds me that some of the stations are quite large with long walks to make connections to another line.

What tips do you have for navigating the Métro?