So many secrets are locked up in the values and edges that I believe that they deserve a careful discussion. Values are the lightness or darkness of a mass. Much has been written about the theoretical side of values but little of the practical.
The practical side of values depends greatly on the use of the value. If one is a photographer, the values may relate to the mechanical limitations of the recording device. All types of photography are based on black and white values even if the final viewing is to be of a photo in color. Film and the digital sensors of today all are based on the capturing of different levels of light which have been separated into there constituent components (i.e. red, green, blue).
We don't see like film and digital sensors record. We see the colors all mixed up and the values are difficult to see. Many times the intensity of a color makes it difficult to classify at which value you are looking. In school I learned to squint at the subject I was trying to understand. The squinting process removes the intensity of color and makes it easier to judge the relationships of the values. Squinting also help us to rank the edges of the values' shapes we are trying to see and the edges are key to seeing the relationships of the values.
Next time you are starting a painting, stop and look at your subject and decide some key issues. Ask yourself questions and study your answers. Most of the answers we understand, we just don't know the proper questions. When trying to get a grasp on values, the first thing that you want to understand is the limits of edge and value.
The answers to these questions will help you to organize your work into something that may not be so overwhelming right from the beginning. Once I have a few of these anchor points, I no longer feel lost and I can start my work with some confidence. I no longer feel that my subject has me lost and I feel I can begin with a clear path in mind. All work should begin with some sort of plan.