This is an excerpt from Gentle Art of Horseback Riding, The by Gincy Self Bucklin.
When you are first learning to lead, in order for you to be perceived by the horse as the leader, your head should be slightly in front of his head—you must be ahead of him—at all times. This is easiest to visualize in terms of the relationship of the horse's head to your shoulder. If you are leading from the horse's left, which is the normal way of doing it, as you look over your right shoulder the horse's head should not go past it. He should also be off to the side so that if something spooks him from behind and he jumps forward, he won't run into you. Later on, as you develop more experience and confidence, you can let a well-trained horse walk beside you or even in front and still have him respect and listen to you (figure 8.2).
While you are inexperienced, if his head gets in front of yours, the horse will feel that he is the leader. If he is feeling timid, without what he perceives as his leader to follow, he might be unwilling to keep going; if he is feeling bold, he might try to take charge. Some horses like to get directly behind you so they can sneak up and nip you, not out of maliciousness but as a horsey game.
Dealing With Resistance
The horse uses his head and neck for balance. The kind of resistance we're talking about is what occurs when you pull on the horse's head in such a way that it interferes with his balance, or he thinks it will, or he feels trapped in some other way. In any case, instead of giving to the pull (and in this case following you), without pulling back actively, he simply doesn't respond.
Your immediate reaction will be to pull harder. This reaction is absolutely wrong for three reasons: First, pulling hard makes the horse feel trapped, so his instinct is to fight or to escape. Second, the horse is far stronger than you, so he can easily outpull you. Third, and most important for you to understand, is that it takes two to pull! If you don't pull, the horse has nothing to pull against and no need to pull. So all you have to do when you feel resistance is to give with your hand or let the rope slide through your fingers until the horse has nothing to pull against. Then you quietly and smoothly try again, pulling smoothly and quickly releasing as soon as you feel resistance.
This would appear to differ from some common training methods where the release comes after the animal gives and not while he is resisting. However, this sort of resistance is not a form of disobedience, so it should not be treated as such. Second, at this stage we are training the leader as opposed to the horse. When learning to lead or leading as a beginner, it's safer to give the horse the benefit of the doubt, stop pulling, reorganize, and ask again rather than to keep tugging until he gives. Think of undoing a hard knot or opening a drawer that sticks. As soon as things feel stuck, you stop pulling, loosen things up a bit, and then try again.
Learning not to use more force when the horse resists is one of the most important skills to develop in working with horses both on the ground and while riding.
Read more from The Gentle Art of Horseback Riding by Gincy Self Bucklin.