Light and Shadow: Lights and shadows help build contrast in the piece to help define the main focus. Without a clearly defined subject, the piece can look undirected, boring, or just bad.
Tonal Range: The range of how light and how dark a piece is. Too much range will make a piece look unrealistic or even straight up bad.
·Three Point Lighting: The three point lighting system consists of lighting your subject with a key light, which is a very bright light placed 45 degrees from the camera, a fill light, which is a less powerful light placed 90 degrees opposite the key light, and a rim light, which is a very low powered light placed directly behind the subject.
·Implied Lighting: Using lights and subjects off camera to cast shadows that fall onto the scene to help develop a piece or the story of the piece in a way not constrained by the bounds of it.
·Back Lighting: A light is placed behind the subject to create a soft and diffused look for the piece to help develop a soft or intimate feel for it.
·Silhouette Lighting: A strong light is placed behind the subject to show just the outline. Can be used to create a hard or menacing atmosphere in the piece.
·Non-Key Lighting: Makes it less obvious where the light source is by using a bouncing light. Can make a piece look more interesting or soft.
A histogram consists of three main areas, shadows, midtones, and highlights, by displaying how much of your picture uses which parts of the tonal range. The higher a graph is towards the left, the more shadows are present in the image. The higher a graph is on the right, the more light it has. If it's high in the middle, the image has mostly midtones. An image usually has one or two spikes in two different areas, and usually a good image won't have them be too extreme.
http://www.techradar.com/how-to/photography-video-capture/cameras/how-to-read-a-histogram-what-you-can-learn-from-your-camera-s-exposure-graph-1320933
