Have one person with a backdrop and one have one light that moves into the following positions.
Light over shoulder- You see that the light from the left causes his face to glow while leaving the right side a bit darker with shadow.
45 degrees to the right of camera- This gives the right side more light while leaving the left side a bit darker while casting a shadow to the left side.
45 degrees to the left of camera- This gives the left side more brightness and leaves the right side darker with more shadow.
180 degrees to the subject's left- This gives almost all the light to the right and leaves the left side almost completely dark with shadow.
180 degrees to the subject's right- Gives mostly all the light to the left side with almost complete darkness and shadow to the right side.
Light on the backdrop- This makes the subject completely dark and gives all the brightness to the backdrop.