Observing and practice are the basics, for us to understand what we’re drawing first but the dynamism you ask is sort of another level? It’s like.. In cooking, everyone can follow the recipe, but it still tastes different when the one who has more passion made it (it’s easily explained as that, I don’t really know exactly how to clear it) it’s more likely “feeling” and “expressing” for your character, it’s what you feel when you draw an angry expression, you also do the same face as your character. For some reason, when you feel the scene of your drawing, you just manage to make those kinds of poses. I guess it’s that?????