Clean the Horse Up First
No matter how great a photographer you are, photos of a messy, dirty horse will not come out looking great. When you're planning to take photos of your horse, take the time to clean your horse up first. At the very minimum, brush off any mud or dirt and untangle your horse's forelock, mane, and tail.
In addition to cleaning up the horse, you want to make sure that any tack on the horse is well-fitting, clean, and flattering. Opt for a leather halter instead of a nylon halter, and use a matching leather lead in place of a nylon or rope lead. If you're photographing a horse under saddle, take the time to wipe down the bridle and saddle, and use a clean saddle pad that won't detract from the photo. For detail shots, take the time to wipe down the horse's eyes, muzzle, and bit.
Be Aware of Your Backgrounds
In cleaning up your horse you've ensured that the subject of your photo is presentable and attractive. But you can't forget about the background of the photo - a busy, cluttered background can detract from the quality of your photo. When choosing a background for your photo, try to find an area that is clean and attractive, letting the focus of the photo stay on your horse. Keep an eye out for potential distractions like power lines, broken fences, jump standards between you and your subject, and other common materials found around your barn.
Looking for a background that can work in your favor? Consider photographing your horse against the solid background of the side of your barn. An open field can also be ideal, particularly if there are trees in the background. A clean arena is also a great place to take photos, but make sure to remove any extra clutter like unused jumps or a mounting block before you start taking photos.
Watch the Light
The source and direction of light has a major effect on your photos. When you take photos, it is best to always have the light behind you. If the light is behind your subject and you are shooting into the light, then you will be dealing with sunbursts on your photo and a very poorly lit subject.
Identify where the sun is shining from and position yourself so that you are between the sun and your subject. This will allow your subject to be properly lit. You will also want to consider what time of day you're shooting at. Shooting in the early morning and the late afternoon is typically best, since it allows you to take advantage of the warm, golden light at those times. This warm light is flattering, whereas the harsh light that is common at noon can wash out your subject and leave your photo looking overexposed. Shooting when there are soft clouds overhead can also help to distill some of the harsher light of midday.
Get On the Right Level
Pay attention to where you are shooting from. Are you looking down on the horse as you shoot? That's often the case, and one simple change that can have a big difference in your photos is to bend your knees just a little bit when you shoot. Bending your knees brings the frame of the photo down just slightly; ideally you want the photo to be level with the horse's body. Watch how your photo changes as you lower yourself down just a little bit, and think about staying even with your horse's shoulder when you shoot.
Don't Shoot Head-On
The very shape of the horse's body makes it difficult to get a great shot, especially when you're facing the horse head-on. Because the horse's body is so long, photographing a horse from the front creates an optical illusion where the horse's head appears much larger than it actually is. While this can make for a comical photo, it is not a flattering look at a horse. To avoid this issue, try to photograph your horse from the side or from a slight angle - never head-on from the front.
When it comes to taking great photos of your horse, practice makes perfect. Try to study the work of photographer you like to see what they're doing. Then, head out to the barn and spend some time experimenting and figuring out what works best for you.