Composition
Line + MassThumbnails
Three two-inch sketches, three values, no lines, three minutes each. Pick the one with the biggest dark mass and the clearest light shape. Commit.
Before any drawing longer than twenty minutes, make three thumbnails. Each is about the size of a business card, drawn in three values only (paper, a mid grey, a dark), with no lines and no detail. Each tries a different arrangement: the tree on the left, the tree on the right, the horizon high, the horizon low, a different crop through the viewfinder. Three minutes each.
Then choose. The winner is the one with the biggest, simplest dark shape, the clearest light shape, and a reason for the eye to go somewhere. A thumbnail that does not read at two inches will not read at twenty. Enlarge the thumbnail, not the subject: the big drawing is a faithful scale-up of the design you chose, with the subject supplying the detail.
Ten minutes of thumbnails saves two hours of a drawing that was never going to work. It is the habit that separates people who improve from people who repeat.
Visuals
Pitfalls
What
Thumbnails drawn in line.
Why
Line shows arrangement but hides the value design, which is what you are testing.
Fix
No lines. Side of the pencil only. Three flat values.