I am working on massing in the beginning of a painting and understanding planes. To help with planes, I purchased one of the planes of the head models and lit it today while I worked on lights and darks. To make this learning less painful, I am painting on canvas paper. If I paint something that I want to keep, I can mount it onto a support after it dries. Otherwise, the exercises can be discarded without too much sadness about the expense.
Dogs are easier than people. Here is a recent commission.