The first step was to use masking tape, to tape off four or more trees, showing correct landscape proportion. Smaller, thinner pieces of tape were cut to create branches. Then the edges of the masking tape was traced with pencil and a horizon line drawn slightly above the bottom of the shortest tree. A watercolor wash was painted in the sky using warm or cool colors only.
During the last day on this piece the masking tape was removed carefully and we added the black "smudges" using black tempera paint and cardboard strips. I found the idea for this lesson on www.artroom104.blogspot.com
My instructional video for this lesson is below.