Setting up early one morning I drew a thumbnail sketch of the Mackinac Lighthouse. When I make my drawing I pay particular attention to the light and shadow patterns. I have found that when I make the drawing rather than taking the time to shade in the dark patterns, I merely outline the edge of the dark and quickly mark the dark with an "s" which indicates a shadow in my artistic shorthand. Proceeding with my drawing I then go on and mark with a "l" my light patterns. Likewise, I use this shorthand further to mark any reflected lights with a quick "rl". I have found this method allows me to work more quickly, which certainly is helpful when working en plein air. This allows me to stick to my initial drawing with the observed light patterns. I have found that a sure way to ruin a plein air painting is to chase the lights or continually paint the lights patterns as they change.
Further, using my thumbnail sketch, I begin my drawing on my pastel paper. Here I am using Pastel Premier paper that I have under painted with watercolor. Typically I select a paper that has the thirds painted horizontally or vertically which ever format I am using. I like to use a yellow underpainting on the top third, a blue underpainting on the middle third and a red underpainting on the lower third. I use a watercolor pencil to mark my vertical thirds. This way I know exactly where my intersection of thirds lie and I can compose with that knowledge. This method of thirds was also employed in my initial sketch so it allows me to draw my subject on a similar format.
After my drawing is all set on my paper, I begin painting the sky. This allows me to layer my pastel application and limits when I have to paint around any object. This is not to say that cutting in with pastel as a correction never occurs. But using the theory that I am painting what is furthest away from me and I then proceed to the middle ground. Artists know that using this method of working back to front also allows the artist now to work over and destroy the already applied pastel. Now even though I am really working quickly keeping my eye on my initial drawing of value patterns I continually step back and survey my strokes.