>>1336197>>1336039>"Figure drawing for all it's worth" by Andrew Loomis>"Drawing the Head and Hands" by Andrew Loomis>"Constructive Anatomy" by Gerge B. BridgmanThis set of books is a good way to obtain solid understanding of anatomy. They might look boring, of course, but they will significantly boost your skills.
>"Force: Dynamic Life Drawing for Animators" by Michael D. Mattesi>"Figure Drawing: Design and Invention" by Michael HamptonSometimes to catch right gesture it's more important for drawing human than even correct proportions, especially for cartoons. And these books are all about motion and dynamics.