Before you start to add the shading, draw the shape of his neck, and then draw the shirt collar. Once that is done you can start erasing all the guidelines and shapes you drew in step one so you can start shading in your Green Day singer's face on the left side. This should be a very light shading. Thicken the shading under his eyes, and under the left nostril. Add some detailing on his forehead, and ear using the same light shading technique.