For those who’ve never been on a horse, here are a handful of things to keep in mind before writing.
Horses are traditionally mounted on the left. This would be the horse’s left side. If you are standing behind a horse, it would be on your left, and if you are standing in front of the horse, it would be on your right.
English saddles typically won’t have a horn for roping cattle like Western saddles, but there are exceptions. Also, when riding English style, the reins are carried in one hand. While riding Western style, they are carried in two hands.
Horses are measured by height in “hands.” This has been standardized to four inches, rather than using actual hands which vary in size from person to person.
Beyond walking, horses may trot, canter, or gallop, with canter being the middle gait. Here’s the Wikipedia entry for it if you’re still unclear on the concept.
In order to ride well, a rider needs to learn how to move with the horse. Keeping ones body in sync with the horse’s gate will help one avoid becoming “saddle sore.”
The term “horsepower” came from a need to compare the energy produced by Watt’s steam engines to that of draft horses.
Complete Horse Riding Manual
How to Think Like a Horse