Three circles and a line. In the past I'd added in some details roughly in pencil to get features' sizes but in the past few days I've given it up. Now I sketch three circles. One for the approximate area of the face, one for the depth of the skull, and one for the nose. Then a curved line bisecting the front of the face to help me with the direction the face is pointing. The rest is up to the pen and any hiccups that may occur on the train as it lurches to and fro or rides smoothly into the next station. It's a bit more fun, I have to say.... :)