Never thought drawing a human face need so much of thinking. Every facial feature plays an important role in each expression. They appear differently in all of the views like - frontal, three-fourth and profile. One has to master drawing the facial features in all of these views. I think there are just two books available dealing with facial expressions to the best of my knowledge.
I have been trying to do a little bit of practice in drawing human faces before I start working on the expressions.