As someone who is horse hunting at the moment – my tip of the day is to use decent photos! I cannot tell you how many adverts I have looked at and discounted because the photos are so awful. Take the time to do it properly or rope a friend with artistic skills to help you out.
I am not expecting the photos to be compositional masterpieces but just a simple full body shot would be a good start rather than the amount of heads and no body or dreadful ridden photos.