Harvey Kurtzman is one of my top favorite cartoonists. I could go on forever about his skills, but I'll start with just a couple important ones to do with character. His characters seem alive. Motivated from within. They aren't tracings of model sheets, or awkward accidental poses.
Here are a couple tools he uses to achieve this.
His characters each individually have direct poses and lines of action, but he goes a step further.
He composes each line of action and silhouette so that the characters dynamically oppose each other. They aren't parallel or mirror images of each other.
Their poses work together to create a composition and contrasts in their attitudes and respective total energies. The character with the stronger pose has more energy and is generally the focus of the panel. The other character is generally reacting to the more dynamic one. He will have less energy - which is described by a less dynamic pose - or line of action.
Harvey makes his characters' poses compose together. The negative shapes between them are beautiful and functional, as they help you see the contrasts in their attitudes.
This quality of being able to draw characters that seem completely alive and moving and progressing emotionally from pose to pose is a rare talent - too rare. It's what you need to be an animator. Kurtzman would have been a natural animator.
You don't see many comics that have this much life. We've come to accept much comic art as being stiff, using repetitive poses and appearing smug in their stagnant repetitiveness.
Sadly, this has crossed over into modern cartoons-expensive ones at that! And leagues of fans defend this stagnation as somehow being an artistic choice, rather than just a lack of knowledge or extreme conservatism. Life essence is now considered "too cartoony".
If you want to improve your posing, life and compositions, then you need this cartoon bible in your library, and you should copy the poses as an exercise every morning before you start your regular work. Then apply this quality of living characters to your own drawings and watch them come to life too.