Beginner artists, take a look at the colored-in areas in the drawing at right. See the curved lines I used in the shadows around the lit tunnel, and around the box on the floor. See how they convey a sense of texture, shape, and the source of the light? Please, when you color your drawings, pay attention to the direction of the lines you draw. You shouldn't try merely to fill a big empty space with quick, thoughtlessly filled in lines of color. Instead, let the direction and shape of those lines show the shape, texture, and shadowing of whatever you're drawing.
For another example, look at the coloring-in of these crocodile faces at left. These crocodiles are colored-in with flat, short, straight lines. Compare those crocodiles' coloring-in to the coloring-in of the crocodiles in the picture below it.
In the top crocodile drawing, the coloring of the big empty spaces uses straight lines that don't show the texture or the shape of the crocodiles. The lines are thoughtless. The artist was just thinking about the color, and in a hurry to fill a big boring space. The coloring-in lines just show color and a sense of boring flatness.
Compare that to this second crocodile drawing. This second crocodile drawing also has colring-in lines in its big empty spaces. However, those coloring-in lines show a direction. They have a curve sometimes, and they show the texture and shape of the crocodiles and the ground around the crocodiles. The coloring-in lines even show hints of where the light source is.
Truman Capote once said, "There are no boring speakers. There are only uninterested listeners." We can say something similar about drawings and artists: "In drawings, there are no big boring areas to color. There are only artists who are bored and hurrying because they're ignoring this chance to show us the texture and shape of the object, and the direction of the light."