It still fascinates me that the more you work on a drawing the better it can look. I always tend to just do a drawing and leave it, even if i think it looks dreadful. However, by building up an image layer by layer you can really add depth to a drawing and keep improving its appearance.
The drawing that i have done this with is very basic but exhibits the point i am making.
By building up the layers, more texture is shown and creates a much more dense image.
This is a technique that i really need to force myself to use more often in my everyday practice, especially on the drawings that i am not happy with.