Since I'm working on a graphic novel I felt it was about time I got myself a good book on how to draw humans in action. "Character Mentor" by Tom Bancroft turned out to be an excellent choice.
Just by browsing through it will give you plenty of useful advices just by looking at the illustrations.
Throughout the book the author points out the importance to use every detail to tell something. To do something about every single thing. The pose, the mouth, the eyes, the neck and even the eyebrows. You don't want your character to be boring and normal, but a character telling us something with its bare image on the page.
Then there is a matter of depth in the image. Here I found a headline about clothes as depth-killers which made me smile, because I have trouble with getting the openings of the sleeves right to fit the directions of the arms. And I just made a leg pointing at the wrong direction.
There is also a chapter about staging the scene, bringing up things like point of view and disposition of a frame.
The illustrations in the book are all the way through very useful and they always tell you something about a new aspect, one that you might not have considered before. The style of them vary some and there is often a good, a bad and a perfect example of something. I love when I get to see what I'm not supposed do, to get a result I'm pleased with; It is very illustrative.
This book is highly recommended.