This needs to be stickied! I'm still seeing threads with poor pictures.
Remember that legs need to be shot from the front/rear straight on. I keep seeing a few that are still at a slight angle. Also be sure there's good lighting in the photo and make sure the background doesn't blend into the horse (such as a black horse partially standing in front of a black doorway). Crouching also helps from taking the photo at too high of an angle.
Helpful website too: http://www.equisearch.com/horses_car..._photo_120808/
And also when taking a picture of the rear legs, take it from the back of the horse where the tail is viewable. I've seen a few where people stick the camera between the horses front leg so you get a leg/sheath view. The POB is an important reference point that can't be seen unless taken from the rear. Haha.