My preference is to work from life. Unfortunately, with most of my subject matter, that is somewhere between impractical and impossible. I generally make photographic studies which I then use as reference material in my studio. These are merely a jumping-off point, and I often combine elements from many different photographic studies, and modify them. I then draw a number of studies until I have the final life-size cartoon.
While I approach every painting a little differently, I usually begin by transferring the lines of the drawing to the panel. I then do a rough, thin underpainting layer, using burnt umber, black, and white. After this, I paint one or two more layers of underpainting in color. Then I paint the final layer in color. With each successive layer the painting becomes increasingly detailed and polished. While most of the decisions are made prior to beginning a painting, often changes are made in progress (note that the buttons on her pants are eliminated after the monochromatic underpainting). I use sable brushes that are intended to be used for watercolors; it is the only way I can achieve the desired results. The oil paintings generally take between two and four months to complete.