The human eye has been referred to as the window of the soul. If you are going to establish mood in a picture a great starting point is the eyes. The first place a viewer is going to look is at the eye to establish story. We look to the eyes to determine if someone is happy, angry, fearful, angry, and every other emotion in between.
In addition since the eye can be used as a system of measurement for the entire face we need to master the anatomy of the eye as a starting point.
Draw the eye below... pause when you need to.