JUST SPEND TIME...
"Just Spending Time" is the most common method actually in use by most adopters.
Given time, nearly any wild horse will become less afraid and more comfortable with people and his new surroundings. The horse may even bond with you, even if that is all you do. And, even if you also use regular training sessions (as described on other pages - Pressure and Release, Clicker Training, Bamboo Pole, etc), some horses need a lot of time to digest their new experiences. Not every horse is amenable to becoming a "90 Day Wonder." Time makes a difference!
Going in and out of the pen while doing daily chores, spending leisure time reading a book in a lawn chair next to the horse pen, just hanging out and talking to the horse - all this will help the horse learn to recognize you as someone who is not a threat.
But perhaps even more important, you will get to know your horse on a deep level - how he reacts, how he thinks, how he lives his life and how he is likely to react to a variety of situations. You will learn to trust him, and to trust yourself with him!
Going about daily chores -cleaning pens, delivering feed, etc., and just leisurely "hanging out" helps the horse feel safe and comfortable around people.
Be careful, though! Just because the horse is not afraid of you does not mean that he is fully gentled or safe to be near!
Eventually, the horse DOES need real training!