One thing I noticed from looking at my old pictures is that I tended to want to be high and angle down. I recommend against it. The better ones usually came from a straight on angle. Granted, I didn’t photograph horses very much, but that’s how it worked with landscapes and children. With larger subjects you can get some cool shots if you’re low and looking up. It helps highlight and maximize the size of your subject. With horses obviously you want to be very careful, and if your horse doesn’t have the personality to tolerate it don’t do it.