I have just seen others doing it in videos, so I knew it was possible, but otherwise I learned my own ways how to do it, slowly transitioning from doing it on-line to liberty, first in a smaller enclosed area, as a roundpen or somethin alike, then moving up to an arena or just the open fields - on a good day we can play in the pastures or walk side by side at liberty in forest trails. To my mind, the key is a horse who is willing to follow, not is taught to follow, so I pay great attention to spending undemanding time with a horse and the whole herd in the pastures and interacting with them as a herd member. And also just taking long walks with my horse, grooming him, exploring our boundaries, my body language and his, and such.
From other horsepeople - Klaus Ferdinand Hempfling really inspires me. He has some books and DVDs, and I can suggest looking into them. I haven't read or seen them in full extent yet, but I really like the bits I've seen and his philosophy as well.
I have come a long way, to surrender my shadow to the shadow of my horse.