accually is very easy... You must just learn to watch and to compare proporcions of a face or body. Just try to compare width of the nose with the width of the mouth, or sth. So first learn to look and watch. The rest is contrast and your imaginat...
This is my blog, so I dont have to write posts here, too... http://jandzithepainter.blogspot.com/
It s in slovenian language, but most important are the pictures, that I publish...