Art books I recommend:
(Many art books contain inappropriate images. Books to be wary of are marked with an asterisk*)
Drawing People* | Barbara Bradley
Probably the best book out there on drawing people. For practice, I just copied a lot of her work to help me loosen up and see things a little differently. Copying another artist’s sketches, style, and practicing anatomical correctness helps a lot in learning the process of drawing people.
Facial Expressions* | Gary Fagin
This has loads of info on the muscles in the face.
The Art of Portrait Drawing: Learn the Essential Techniques of the Masters* | Joy Thomas
One of my favorites on strictly portraits. There’s also a neat drawing of a skull that I copied. Very helpful.
The Book of a Hundred Hands | George B. Bridgman
Copied several pictures from this book as well. Lots of little bones, muscles and tendons!