Start with the face by tracing your sketch with the Pen Tool (P).
The face comprises half of the head and one ear. You can draw portions of it (head, jaw, and ear) separately and Unite in the Pathfinder panel.
Either set the stroke color to dark brown in order to create an outline, or Copy (Control-C) and Paste (Control-V) your face shape, set the fill and stroke color to dark brown, Stroke Weight to 2 pts, and Align it behind the original face.
Draw a small D-like shape for the other ear, in a darker flesh-tone (relative to whatever flesh-tone you've chosen) and place it behind the other head shapes. For more info on various skin-tones, check out this quick tip from yours truly.