The rules of drawing facial expressions are the same as for drawing the human form. The important thing to remember is that you must learn to see and represent areas of light and shadow rather than indicate facial expressions with line. Learning to draw is about learning to differentiate these areas of light and dark and reproducing them accurately. In a drawing, a smile, a laugh, a frown or a pout is made up of abstract shapes. To re-create these shapes well, make sure you have some good heavy drawing paper with a high rag content, as well as a set of quality drawing pencils.
Set up your drawing using a very light, fine line. Use an art projector or light table for greater accuracy.
Fill in the darkest areas of the drawing. Pay special attention to laugh lines around the mouth, lines around the eyes and any other areas that indicate facial expression. Fill in the eyes, nostrils and area where the lips meet.
Fill in the midtones of the face. Look around the mouth and eyes. What sort of light and shadow exists there? Where do you see stark shadows, and where do you see fine gradation? Are the lips slightly upturned, or are the eyes creased? Representing these areas of light and shadow properly will help you render the expression properly and create a more faithful portrait of your subject.
Begin to work in areas of finer shading. This includes any very light areas on the face and any areas of graded shading you may have missed. Look at your portrait carefully to make sure it re-creates your original.
Go over your drawing with a chamois cloth or tissue to blend in the areas of shading. Use caution with this procedure since it can smudge your drawing.
Use an eraser to work in the highlights on the face and hair. If this leaves too much of a fine gradation in some areas, draw the details back in with pencil.
Look at your drawing, comparing it to the original. Troubleshoot any areas that don't look right. Making a scan of both your original and your drawing and looking at them side by side on the computer can help. Reduce your original to gray scale to get a better idea of how it compares to your drawing. When examining your drawing, try to see if both the expression and the emotion are properly represented. Does the smile look like a smile or a grimace? Do the eyes look like they're laughing or squinting? Keep working until the facial expression looks right.
Spray your picture with fixative to prevent smudging.