The upper lip is wider than the lower lip. Shade the upper lip and add a
patch of shadow below the bottom lip.
Novice artists often stumble at the profile—specifically the lower
half of the face. It’s an area that requires a little troubleshooting. The
outline of the front of the face below the nose is never a flowing line;
it’s a line with many abrupt shifts in angles. Even the lips possess their
own separate planes.