Part of it involves moving towards the idea of examining the actions that a character is performing and imagining it fully in your mind, then translating that onto the page or canvas in a series of steps. There's a plethora of techniques for illustrating a sense of movement or impact or general force (most of them involve hatch work. Japanese techniques are, I think, generally accepted as the most effective, but it's a lot more complicated than "speed lines").
You'll need to understand not just where the action is in the moment that you choose to illustrate, but also where it came from and possibly where it means to go. That way you can add secondary movement and choose where to direct the focus of the composition.
Good motion, like most things in illustration, come along with practice, and the techniques are easier to practice when you've got strong underlying structure to base them on. Perspective practice will help you set your characters in a physical environment, and in doing so you'll get a stronger sense of how the character has/is/will move around. Composition practice will help you frame the action most effectively.
I hope some of that made sense, anyway...