Before we start drawing the mouth we need a quick measurement of the whole face.
It's important to note that when you draw out your basic guidelines that you should intend to erase them... especially your initial oval for the face shape. Remember it's what in the inside that counts. So in order to have your final face shape you'll need to draw the eyes, nose, and mouths first.
The measurements above give you basic anatomical guidelines to approaching the face. So far we have learned how to draw the eye and the nose. You cannot find where to draw the mouth until you finish drawing the eyes and nose. The eyes should be one eye apart.
In fact, the eyes can be used as measurement for the entire face. The face is actually 5 eyes wide. The space from the bottom lip to the chin is one eye. So in order to find where to draw the mouth will be dependent on the eyes. The mouth actually fits between two pupils. So in order to draw the mouth on a face you will need to draw both eyes first.
See how the mouth lines up to the pupil?
Above is a basic drawing tutorial for drawing the mouth. Notice the upper lip is darker than the bottom lip? This is because most light sources such as lamps, ceiling lights, or the sun are above our heads.
An open mouth can be trickier sometimes. It's critical that you find the centerline of the face in order to start drawing the teeth. Also, note that the upper teeth are larger than the bottom teeth.
The mouth can come in a variety of shapes.
Always remember that mouth, eyes, and nose are connected to a skull underneath.
Here are some more sketches that can be helpful for your face studies.