This is a great way for beginning art students to get value established. You'll need a mirror, a black and white medium (here I used marker and white acrylic), and some clear acetate or plastic wrap.
1.) Place the acetate or plastic wrap atop a mirrored surface.
2.) Stand in our reflection, very still mind you, and draw on top of the shadows.
3.) Next paint in the highlights.
Once you have finished you can go ahead and use your drawing to plan a mask design, paint atop and develop details, add color, tissue paper, or pattern. You may even want to photocopy your work.
Set the clear acetate atop a mid-valued paper in order to get the highlights and shadows you're looking for. This is a great way to get students away from caricatured drawings of themselves, without having to tall their friends not to move. The next time they go to draw a model, they'll understand what it takes to sit still!