I started by finding a young horse who had been well handled and given good boundaries from birth! He is already very trusting of humans and respectful too. Currently I am building on that using daily handling: grooming, leading in hand, desensitizing, etc. He is only fourteen months old, but seems far more mature in his attitude. Yes, he sometimes has spooks or "looky" moments, but he always pays attention to his handler's cues and responds accordingly.
For example, before he was gelded, he was sometimes coltish: he would call to the stallion and his field buddy - another colt - and jog about at the end of his lead rope. For maybe 5 seconds, lol! As soon as he got an "ah-ah!", he would settle and pay attention again.
He panicked and did a little half rear once, and I stood calmly and quietly: not about to get into a tug of war with him. Well, he dropped his feet back down where they should be and stared at me. "Get along then," said I, and I swear he just sighed with relief that his human was calm. Ambled along on a loose lead all the way after that. Has never done it since.
I feel very lucky in that I have been able to continue working with him alongside the people who raised him. So he has gotten used to me in familiar surroundings, which I feel has made the change of ownership go far more smoothly. Basically we weaned him slowly from one human to another. In my opinion, this has really helped with our bond. I have also made sure to be there every day. It is a round trip of thirty miles for maybe fifteen to twenty minutes handling, and a spot of mucking out/hauling water/hay/etc. But it is worth it! My little guy comes running to the gate when he hears my voice.
We will be moving him to a new barn this week. The seller is transporting him there for me, and he will be growing up there. The seller has also invited us to go out showing in hand with them next year, which will be a great opportunity for both me and my youngster!
I plan on starting him under saddle when he is four or five, but will be introducing the bridle earlier, and doing a lot of groundwork along the way. He is my horse of a lifetime, so I have no wish to rush with the foundation stuff.
A moment of patience is worth an hour of wrath...