After you have decided on location and whether or not you will be in the photos, and have prepared yourself for the photos, spend enough time to have the horse prepared. It's not just about the grooming; environment and even some training should be considered.
Have an idea of what type of images you are wanting or needing. Do you need some conformation images for advertising, or are you wanting some more personal images of the bond you share with your horse? What is the tone you are trying to set for your images: something more traditional and conservative, or something more dramatic? Letting your photographer know your expectations is extremely important. Pinterest is an excellent site for creating some inspiration and getting some ideas. Share this with your photographer. I love it when the customer knows what they want, but still allows me to use my ideas, too.
To make your session with your horse less stressful, work with your horse before the session. If you are needing conformation photos, you will need to teach your horse "whoa" on the lead. Horses are trained to follow us, so when we walk away to get out of the picture after getting the horse set-up perfectly, the horse will follow. A little work days/weeks before the session will help prevent them from doing so. Another thing to consider in conformation images is the profile. Horses are trained to stand square for halter, but profile shots where the horse is standing square can give the appearance that the horse only has 2 legs (fig. 1). Teaching the horse to stand with some separation of the front and back legs (fig. 2) will look much better. Know your horse's conformation flaws and best features; too much separation, or not enough, can make these points better or worse.
Correct set-up for showing, but not
suitable for photographs as it gives the horse the
appearance of having only 2 legs.
Correct set-up for conformation images.
You can see all 4 legs clearly.
If your photo shoot is for a group of people at the same barn and the images are to be used for advertising, put someone in charge of coordinating the shoot. Having a cohesive look will greatly improve the look of your ads and photo groups. This can be in the details of grooming, tack, and outfits. Grooming and tack should match the attire of the riders. You can even get as picky as having the same shades of leather. Outfit colors should coordinate with your horse as well as with others that will be included in the photo collection.
Another detail to consider is tack. Clean your tack before the shoot, even if it is just a quick wipe-down. I prefer leather tack in images. A brand new, bright nylon halter is very distracting and brings the focus of the image to the halter, not the horse. With the exception of conformation shots, horses that are too young to be ridden, and halter horses, I think a bridle looks better and allows you more control.
Again, consult with your photographer: good communication can lead to the start of great results!