You want to sketch in the action and approximate location of the hand, fitting each part as it appears. Next solidify, or construct the shapes-the block method of drawing the hand is of great assistence in defining the planes and surfaces of the hands and fingers. Next start to add the details. Carefully add the details of the hand and fingers erasing the first two steps as you go, and as they are no longer necessary, or they have already served their purpose. Finally, add the tones, or light and dark planes.
Reflective light applies here, so long as the shot calls for it.
Memorize this stuff, get an anatomy book, and study. You will never stop studying the hand as you will probably never draw the same hands in the same pose twice. Every shot is a new lesson in hand construction, and a new journey or exploration into a great adventure of expression. Again, the hands are equally as important as the face. They require equal importance of attention and study as the head.