Horse Clippers - ALL
Although many horses never see the blade of a professional horse clipper, halter showing requires (at a minimum) bridle path, ears, nose, under chin, around the fetlock and hoof area. During the winter in hunter circles, full body clips are common. Clippers can actually help you "sculpt" the perfect horse. Judicious use of a blade can make your horse's ears more elegant, his head more refined, his white socks shimmering white.
Understand your blades. The higher the number of the blade (ie:#30 or #10) the deeper the cut and the shorter the hair. A #40 blade will take the hair all of the way to the pink skin. A #10 is better for blending from deep to top coat using less pressure as you blend. Some clippers come with extra wide blades (T84, T10, Wide 10) to make clipping faster and smoother. The faster the blades move (spm), the smoother the cut and the fewer the tracks.
#30 and #40 blades are good for bridle paths, ears and muzzles; #10, T84, or wide10 for the rest of the horse. Use a #10 to clip against the growth of the hair on white socks, powder with white chalk or cornstarch and get flashing white stockings.
Ears can be a challenge. Don't wait until a day before the show to start. Get your horse used to having his ears clipped months before showing when both you and the horse are relaxed. Start with the back side of the ear, gently allowing him to get used to the vibration before you move to the front inside.
It is a good idea to have a strong, full-body-capable clipper and a cordless trimmer for hard-to-reach areas like the hairs at the inside base of the ear.