Photography is about light...you always hear that part of the equation, but photography is also about shadow. Make good use of the shadow areas of your portraits as they help direct the eye to the light. In most any image, your eye will go to the lightest or brightest part of the scene, use that knowledge to guide your viewer to the most important part of your picture. This portrait of actor Jerry Grayson is a good example; your eye goes right to his face and his eyes. Also, notice how his lighter color shirt forms a "V" pattern, leading your eye up to his face.
Actor Jerry Grayson, photographed in his home in New York.