One of the most complex exercises when you are studying animation is a walk cycle of a four legged animal (in this case a horse, but you might take a dog, a cat). This is why you must be aware of every single part of the animal while you are drawing because all of them are moving at the same time. Legs, spine, neck, head, back. That's the Traditional Animation.
PLAY WITH IT
Download the frames of the horse gallop and make your own animation!
(24fps. 2 frames per each)