Seeing your scene as a painting and design is key to read-ability. Also, limiting the amount of big shapes or areas of value helps simplify, read clearer, visually has greater impact, and forces you to think about shapes and design.
In this one class lesson, Ray stresses the position of shapes, the amount of space, and contours of shapes to keep the viewer interested. Changing one shapes effects another so lets follow and learn how to avoid the ever present pitfalls in this demo-paint-along.