Marks
Line + MassGhosting a line
Rehearse the line in the air three times, then land it once, moving from the shoulder and looking at the end point.
A straight, confident line is a motor skill, and like all motor skills it is learned by rehearsal. Mark a start dot and an end dot. Hover the pencil over the start, and swing it along the path to the end three or four times without touching the paper. Then, on the next swing, lower it and let it land. Look at the end dot the whole time, not at the point of the pencil. The hand goes where the eye is.
Move from the shoulder with the wrist locked. A wrist pivot makes an arc, and a wrist-drawn long line always curves. If a line must be longer than your forearm can comfortably travel, turn the paper rather than bend the stroke.
Ghosting is not just for straight lines. Ghost the curve of an arch before you commit it. Ghost the big sweep of a tree's silhouette. Every deliberate line in a Cotman or a Roberts was rehearsed in the air first; that is why they look inevitable.
Visuals
Pitfalls
What
Hairy lines made of many short overlapping strokes.
Why
You are drawing with the fingers and correcting as you go, which the eye reads as hesitation.
Fix
One stroke per line. If it is wrong, draw another one beside it rather than patching it.
What
Watching the pencil point.
Why
The hand steers toward wherever you look, and the point is behind the destination.
Fix
Eyes on the end dot before the stroke begins.