In the last year or two of learning to draw, I've accumulated a number of art books. Here are some particularly good ones for beginners.
Kistler, You Can Draw in 30 Days
Very friendly, exercises that don't take hours on end, and a concise list of drawing principles on pp. 2-3.
Dean, Animal Line Drawing
You can crank one of these out in a spare moment and it will look reasonable.
DeWilde, 30-Minute Drawing for Beginners
More short exercises and principles.
Howard, 101 Textures in Colored Pencil
This is more of a reference, but drawing these will get you in the habit of layering colored pencil to produce rich textures.
Bower, 101 Sketching Tips
A long list of clever tricks and observations for sketching from life.
The Sketch Encyclopedia
Some mediocre general advice followed by a HUGE catalog of things to sketch, each with four reasonable stages.