After you feel like you've gotten decent control of your mule in the halter and on the lead rope, you can start to work on a little more desensitization. The spots that Ty likes to really focus on are their legs and blind spots.
Now it's time to put the saddle on. If you've done a decent job with desensitizing and halter driving, you should have no trouble with this. After getting the saddle on, make sure you incorporate the exercises you see Ty do in this video to make sure your mule/horse is comfortable with having the...
The next thing that Ty likes to do to prepare his mules for a successful ride is to work on lateral flexion. You want them to be able to flex to the left and right smoothly. It's important to note that you do not want to force this. Simply fix it up, and let him find it.
Now it's time to start ground driving. Make sure you have enough rope to put some decent distance between you and the mule. Ty will start off this exercise with a halter, and then he will work his way to using a snaffle bit.