Chris Sims has played roleplaying games for 30 years, and he has helped produce games for nearly 10. Before he laired in the Seattle exurbs, he was an editor/designer at Wizards of the Coast. There, he worked Duel Masters, Dungeons & Dragons, and Magic: The Gathering.
This book is so helpful. I am a freelance graphic artist using a computer to create my art. I have never been able to put a pencil to paper and draw anything other than a malformed blob. This book has lots of useful information and great advice to anyone that is having trouble with the most basic of techniques, drawing a straight line. Also helpful is the advice given on perspective. A painting by Van Gogh is used as a reference to demonstrate how to identify perspective lines.
I spend a lot of my time graphing algebraic equations. I know that sounds silly and insanely boring, but I do it, not as a hobby trust me. I know that I need a ruler to graph from one plot point to another because drawing a straight line is not easy.
Now I realize art and algebra are entirely different unless you are writing code to generate fractals, but if just drawing a straight line on a graph is hard, imagine how hard it is to do so artistically. In "Learn to Draw - Line and Perspective..." Chris Sims explains that straight lines do not exist in nature and therefore are difficult to draw. The longer the line, the more difficult it is to keep it straight. Sims does a great job explaining lines in art and also stresses the importance of keeping your subjects in perspective to each other. This is indeed a beginner's guide, so don't expect to read it and suddenly be Van Gogh 2015, but if you are an absolute beginner, this is an excellent book to get your started.