Yeah, lighting, colors and forms, those things can get difficult. It takes a lot of studying to really develop a feeling for ambient strength and color (references help a great deal) and then form and lighting. The classic breakdown into simple shapes, when you imagine the lighting, really helps a great deal. The extra kicker, then, are the drop shadows! Imagining them is a beautiful game, though. You really get to school your imagination and spacial visualization.
So, in your mind, breakdown complex shapes, like people, faces and all of that, into simple geometries, so to say: cylinders, spheres, boxes, cones. When you do the lighting that way, you then can "carve in" the details.
