Thanks for your feedbacks, I appreciate them very much. As you can see, I keep progress of my drawing from the first stages to the finished portrait. The best advice I can give you when drawing a face is - particularly a well known subject - don't take any creative license. Try your best to achieve a faithful layout of every detail and that includes tiny hairs, eyelashes, specs of lights and shadows. I don't throw lines around and do not add more to my sketch than required. By keeping my drawing as neat and as clean as possible, I have an exact blue-print of how the complete work should look like. My main concern are the eyes, if I capture the look, then I move to the nose, mouth, etc...Once the face is finished, I shade in the rest of the body and finally the hair. Before you are done with your drawing, check every detail and try to match the values of the original as best as you can. A drawing can be very good, but unless the shadow areas are strong and dark as they should be, it lacks punch. Don't be afraid of using dark tones, I know it can be intimidating, but if you start gradually, you will find it that it gets easier with every new drawing. I use Strathmore 500 Series 30x40 and Derwent pencils from H, HB to #8.