The Diagonal Line is a line of energy and movement. It is a line that slices diagonally through an image and leads the eye into the frame. You can use them to create a strong impression of movement or you can use them to create a tremendous sense of depth.
In my way of thinking "working the scene" is in reality working the composition. It can be very easy to become fixated, or locked into, a particular composition. Perhaps it is something you have pre visualized or you feel the composition is so strong that you feel compelled to wait it out for the right light.