Ron Johnson, a Cincinnati oil painter, lends this advice for success at defining the major shapes and colors in your landscape composition in his article "Finding the Right Subject" in the March issue of The Artist’s Magazine. (This step comes after he’s made a simple sketch of the composition, checked the proportion and perspective, and edited out extraneous elements.)
“During this step, I usually squint my eyes to remove color and subtle value changes from view; this helps me see the major positive and negative shapes. Try to forget what the object is and see only masses of color and shape.
“Then choose the brushes you want to use. I like to use a #4 flat bristle brush, but if the paint isn’t doing what I want or the canvas isn’t being covered the way I like, I might use as many as five brushes of varying sizes and shapes.
“Next, I pick my darkest shape and mix a dark, thin color with odorless paint thinner. I paint medium-value shapes and paint their general color. For example, the grass shape is green, but the tree line in the background is a different shape and shade of green. I see these as two different shapes and elements of the painting.
“Then I paint the lighter-color major shapes, avoiding the use of white early on, if possible. At this point, the majority of the canvas will have some paint on it. The major shapes and colors of the composition, in general, will have been painted with some degree of accuracy—with good drawing and color. This is considered the block-in. Now you can start defining the painting’s subject."