Check out the 7 games of parelli! Also you can do desensitizing (Clinton Anderson method) with plastic bags, tarps, ropes, anything really. Try join up as well. If you are unsure of any of these, look them up online! Videos really help!
I had a lot of trouble forming a strong, mutually respecting bond with my first pony (a mare that hadn't been really ridden until seven) and found the Parelli methods and ideas to be extremely helpful!
I work with my horse after every ride on ground work, manners, space etc. I use lots of different "scary" things to make your horse/pony trust you more, such as tall flower boxes, poles, tarps and I show at A and AA all the time, it's outside of glamorous shows it more about bonding and how you speak and quite frankly I taught my pony how to bow, we're working on smiling on command, and it has REALLY helped him work with me more when jumping and riding, because your voice will help them understand it's okay! I found what really helped my horse, because when we got him he had no trust in his riders, he is only 7 , almost 8, got him whenever he was 7 and these few months have really helped! I've had him for almost 10 months and the little guy has changed his attention span with riders and how he is around the barn A LOT. Bottomline, weird "scary" exercises and stuff like that makes them really trust you, and different atmospheres like trails and stuff like that!