The way I usually begin to draw a portrait is to let my pencil or charcoal lightly wander responsively into every nook and cranny of the head without stopping to focus on details. In this way, I get a feel of the attitude of the head and the location of the features. Then I begin to develop the eyes beginning with the eye that is closest to me. I really focus intently on that eye with no consideration of any other feature. I look at the small shapes of the whites aroung the iris and examine how they relate to each other reletive to the orb of the iris. Is one corner higher than another? What is the horizontal alignment of one end of the eye to the other. I then move the other shapes surrounding the whites and the iris and carefully develop each shape until all the shapes within the eysocket are completed to the satisfaction of my eyes. I then move to the other eye paying close attention to the space between the eyes using the eye I just finished as as a measurement guide and complete it in a similar manner. I pay close attention to how each eye lines up with the other horizontaly. I compare the size of the second eye to the first until I am satisfied that they are correct. I now have a series of shapes that I can use to align and measure the rest of the features with. I work outward toward the sides of the head. This gives me the relief from being cramped within a fence. From there a good likeness is almost assured.