good trainers tend to be kind of expensive but you can learn alot even by going and watching trainers with other horses. The principles of horsemanship once you understand the brain of a prey animal can be applied to fix a variety of problems.
When you realize the why then its easier to communicate to your horse what you want done in a way that he can grasp it easier.
"For I know the plans I have for you," declares the LORD, "plans to prosper you and not to harm you, plans to give you hope and a future." Jeremiah 29:11