Step 1: Build the Shape
To begin you will use your styrofoam ball as your base. Build on features by pressing modeling clay onto the ball, making sure that the edges are well pressed into the styrofoam. Be creative! Just keep in mind that by the time the head is complete these features will be both bigger and less distinct, so exaggerate.
When you have created your shape, cover the entire head with aluminum foil. Press this on as tight as you can to your features, and try to do it all with one piece.