CGCookie - Shapes, Forms and Contrast

https://cgcookie.com/courses/shapes-forms-and-contrast

Everything you create as an artist can be broken down into a shape or a form. There are four basic shapes which can be turned into forms when depth is added, creating an illusion of a three-dimensional object. Once you know the four basic forms, you can practice the analyzing and breaking complex objects down into these forms. This is incredibly valuable and you will later use this skill to understand lighting and shading.
Shape language is another important aspect of digital painting and it can reveal a lot about your subject. In character design, a whole personality can be defined by shape alone. Next, we take a look at contrast, one of the most important aspects in digital art. Determined by the difference in color and brightness of an object, contrast can be soft or hard depending on which brushes you use. Artists usually aim for a balance to create a realistic look.