Interpretation partly depends on whether the face represents the self or someone else. The simple 'circle' face is a motif from early childhood, with a genuine 'smiley' suggesting a happy-go-lucky nature. Beautiful faces are often drawn by girls, some analysts suggesting that these are idealised self-portraits. A beautiful face can also indicate a sociable 'people person'. Conversely, ugly faces can might indicate dislike of people and a bad temper, but can also reflect experiences with cruel or threatening people, or of media featuring archetypal ugly characters such as witches or trolls. The notion of beauty is of course highly subjective, and dependant upon artistic skill. Doodles are often abstracted, although some keen artists are able to draw quite realistic faces with the lack of focused attention that a doodle usually implies. Cartoons are artworks rather than doodles.
Eyes are a favorite doodle. As "the window to the soul" they carry a great deal of expression and meaning. As a creative challenge, they may also suggest a frustrated artistic talent. They are sometimes regarded as showing a wish to be desirable. A feeling of being watched might be shown by a staring eyes, or especially an eye through a keyhole - you feel your privacy is being invaded. In traditional symbolism we find the eye of Horus with a modern interpretation of protection, and the eye of Providence representing the all-seeing eye of God.
Doodles of voluptuous lips might indicate frustrated desire. Frustrated artists also draw features of the face in isolation, as they are often pleasing to draw individually though difficult to fit together correctly - see this lesson on drawing the mouth.
People - Figures and Stick Figures:
Stick figures tend to indicate artistic development being stalled very early. Interpretation depends on the amount of detail, who the figures are, and what they are doing. More complex figure drawings require a lot of thought, and begin to leave the realm of doodling and become artwork (conscious drawings, rather than absent-minded doodles).