Mouths
You will approach drawing the mouth the same way as eyes and noses - focus on the larger shapes, shadows and highlights then work your way down to the details.
What you're being graded on:
You have at least 3 mouths drawn - the one below and two from other angles.
You use photos of real mouths - not other people's drawings.
Your drawing is shaded and the mouth, lips, etc. have volume that creates a 3 dimensional look to them.
You can start with a rectangle roughly the size of the mouth. Divide this into 4 sections.
Lightly sketch in the shape of the top and bottom lips.
Lightly shade in the top and bottom lips. Notice the lines used also go in the same direction as the ones on the lips.
Continue slowly shading and building up detail.
Add the shadows and highlights around the outside of the mouth.