Most of the city is laid out on a grid, which makes it easy to navigate. Namsan Tower makes a good point of reference from many places in the city.
Subway stations make a convenient point of reference for pedestrians. The exits of each station are numbered. If you get lost, just find a subway station and look inside for a map. You’ll find a map of the area, which will show you the area around the stations, and which direction the surrounding stations are in for point of reference.