"No More Flat Faces"

The head is a modified oval with several flat planes.  As you shape the head you'll want to correctly capture the basic shape and form of it before carving any details; the protruding nose, the recessed areas for the eyes and most importantly, the shape of the lower half of the face.  It is the horseshoe curve of the dental arch that defines the jaw area.  The curved shape of the teeth, the dental arch, is shown in red on the drawing.  On my roughed out shape of the head at the right, notice the angle from the chin back toward the cheeks.

Looking down at the face from above you'll want to have a 90 degree angle from the tip of the nose to the cheeks. This will allow you to properly shape the nose.  Only half of the nose actually extends forward of the face because of this configuration.>

The detail knife is used for the "smile lines".  When shaping the mouth area, think of the lips as being wrapped around a cylinder.

From the side view, the upper lip is slightly forward of the lower lip.  The location of the lips should fall along a line drawn from the tip of the nose to the chin.  Notice too that the wings of the nostrils do not extend forward of the face.

And  here is a picture of the lower half of the face which, because it is a photograph, looks flat, but we know it isn't.  Now you can go ahead and add the other features knowing that your finished head will be carved "in the round".