The Shire is the Great Horse of England. Shires were originally developed for use as heavy cavalry chargers to carry knights in full plate armour. No longer used extensively as either cavalry chargers or work horses, they're now returning to their original role as heavy riding horses.
The Shire is one of the largest and tallest breeds of horses in the world. The Shire Horse Society requires stallions to be at least 17 hands (or 5 feet, 8 inches) at the withers, and mares, 16 hands, but quality Shire mares can be 18 hands (or 6 feet) at the withers and stallions even taller. Their great size means they have different requirements than smaller, lighter horses.
Groom your Shire carefully. Grooming a Shire is similar to grooming other horses: time spent lovingly on your horse, cleaning it thoroughly. However, a Shire's great height may require you to use a stepladder or stool to make sure your horse's poll, the part of the head just behind its ears, its neck and its back are very clean; the mane should be lying smooth and flat. Dirty, matted hair in these areas subjected to the weight, sweat and friction of saddle and bridle will hurt your Shire. If your Shire has feathers, or long hair on its lower legs, spraying them with detangler will help you comb or brush them out. Dirty, matted feathers are a breeding ground for infection.
Tack up your Shire with a bridle and saddle that fit. Shires are not only taller than most horses, they're far more powerfully built. Even bridles sized for big "warmblood" horses may not fit your heavy draft horse. Proper saddle fit is imperative; a saddle that's too small will hurt your Shire and may cause permanent injury. When buying a saddle, consult with a trained, professional saddle fitter. Although the right saddle for your horse is money well spent, if it's currently beyond your means, ride bareback or with a saddle pad rather than with an ill-fitting saddle.
Lead your horse to a mounting block and mount from the block, rather than from the ground. Shires are known for their calm, gentle dispositions and they seem to be less physically sensitive than "hot-blooded" horses like Arabians and Thoroughbreds. However, hauling yourself up some 5-1/2 to 6 feet from the ground will torque your Shire's back. Don't do that to your horse if you can help it.
Ride your Shire quietly until you're used to its movement. True to their origin as heavy cavalry chargers, Shires can be very athletic trail horses, dressage horses and even jumpers. However, because they're still mainly bred as draft horses for hauling and ploughing, Shires tend to have more "action" than many horses bred specifically for riding. Combined with their broad backs, their rougher gaits make them a very different ride than Arabs or Thoroughbreds, which have a flat, smooth action. An exercise program to strengthen your legs and increase your flexibility, particularly in your hips, may make riding your Shire more comfortable for both of you.
If you use a step stool to groom your Shire, it should be solid and steady.
Always wear a helmet when riding. The calmest, kindest horse can still be startled or trip, and a fall from a Shire can result in serious brain trauma.