I thought this video i made of my other horse at liberty last spring might be helpful.
I do a lot of desensitizing, yielding the HQs, and yielding the forquarters. It also shows me stepping in front of the drive line to get her to change direction. I'm a big follower of Clinton Anderson, because he is just a very good at teaching. His fundamentals series is really what gave me the knowledge i needed. Eliza At Liberty - YouTube
Feel free to message me if you have more questions. :)