I have hip problems from running XC in college 2 years ago. What I always find helpful are the butterfly stretches where you sit down and put your feet together in front of you so your legs look like butterfly wings and push down on your knees. Also what I was told at school was to work on my core strength because everything in your legs is attached to your core. Another thing I was told was that a total lower body stretch was good. So stretching out your hips, quads, hamstrings, calves, etc. really gets you nice and loose so to say. I have found that all of those have helped me.
Your horse is an extension of you.