Value and Shading Practice
Light and dark are what make a drawing look solid. Outlines alone always look flat.
A munkamenet hossza
Beginners draw outlines because an outline feels like the real drawing, and then wonder why the result looks like a sticker. What makes something look solid is not its edge, it is the range between its lightest and darkest parts.
The usual failure is timidity: everything ends up in a narrow grey band in the middle. A drawing needs somewhere genuinely dark and somewhere left completely alone, and beginners routinely stop two or three steps short of dark enough.
The other habit worth building is shading in one direction rather than scrubbing back and forth. Scrubbing produces an even grey, which is precisely the thing that makes a drawing look flat. Lay strokes the same way and build depth in passes.