If I want to take it a step further than the small sketch, I can lay out a value sketch on my canvas, using a mix of alizarin crimson/ultramarine blue thinned with paint thinner. This is done very thinly. I use a rag to rub off most of the paint and just give me my drawing with the values as a stain to the canvas. Alternately you could use burnt sienna for the value sketch, but I don't typically use a lot of earth tones on my palette.Â Here's the canvas value sketch I've done as the first stage of my painting:
I won't always do this detailed a drawing to begin, but since this scene is more complicated than my straight landscapes I thought it might be a good idea. When painting en plein air, it is a good idea to sketch out your composition and suggest some values perhaps, but the light changes so quickly that I wouldn't do this much detail at the beginning stage unless I could return to the same spot at the same time of day on subsequent days.