After the foundation has been laid and basic groundwork is taught to the horse, I can then begin saddle training. Introducing the saddle can be a scary and unnatural thing for a horse, so I must show him there's nothing to be afraid of, This is why I do the groundwork first, so he trusts me and I can build off of the skills he has already learned.
I start by desensitizing with the saddle. To do this, I might start with it on the fence and sending him between me and the saddle, resting him when he bravely looks or investigates it. Then I might start flapping it around closer to him. Eventually, I will have sacked him out to it enough to where I can place it on him with a foot rested and head down, totally unphased by it.
Once he's comfortable with it making noise, and it being around and on him, then I can move to rope and cinch pressure. I will get him used to a back and front cinch. Most horses will buck the first time they experience this pressure, it is totally normal. That's just them trying to figure out what it is and getting used to it. I will roundpen him until he no longer bucks, and then ask him to com in to me and rest. The horse is only allowed to buck for one day. That's it. If he were to buck with it the second day onward, I would make him work for it by moving his feet and changing directions strenuously.
One of the exercises I practice religiously with these horses in the first stages is called the "Human Curry Comb". This involves laying over the horse's back and acting as a sort of brush, petting, rubbing, and scratching the horse until he doesn't react anymore. I will shift my weight, swing my legs, make noise, doing anything to sack them out as far as possible. I will eventually get to the point where I can jump on with no reaction and slide off of the hindquarters. This is a crucial step in getting the horse used to a rider's weight and movement.