I barely started haunches in before I had to put my gal on break for the winter, but we had already done shoulder in. Making sure you have a good shoulder in before starting with the haunches will always give you a good base, as well as working with the movement from the ground. That's how I started Terry with it, actually. On the ground, take a long whip or hold the stirrup in your hand. I find the whip goes over easier because you can correct things across the whole body. With the whip or stirrup, mimic the cues you would use if you were undersaddle. From the ground, you have more ability to baby the horse and give rewards for the small things they do-- you can see their movement and reward steps in the right direction.
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Besides that, when you ride for the haunches in you basically flip over the cues for shoulder in. The first round of attempts won't be perfect, but just reward inches in the right direction. If they respond a smidge better to the cues, reward. If they keep a better bend, reward. Blah blah blah. Good luck training! :)