One big tip I've also read is to get them out of the cage/pen or at the very least get the pen/cage out of the photo. From all the times I've read of rehoming animals they biggest success rate comes when the animals are shown in a happy environment (eg running outside on the grass, no fencing in sight) and/or in a happy home like environment (a coloured, patterned cushion to sit a kitten upon, or a couch for a dog etc...). In other words showing the animal as it would be in the future owners home, as opposed to showing the animal sad and alone in the kennels (because at the end of the day people want to buy the loving, happy animal as opposed to the sad one - they feel sorry for it, but they don't really want to take it home as much as the happy one).