You first need to master the trot and the walk before you try to gallop on a horse. The key is to remain in control at all times, you first want to develop a stride, as the same rhythm is used in a gallop.
Before galloping, it is recommended that you raise your seat, keeping your back straight and your weight properly distributed on both sides of your horse. Now, shift your weight in the heels which will force the horse to quicken the stride. However, you should never dig your heels forcefully as this will startle the animal.
For your own safety, hold the reins firmly in both hands keeping the width of the horse’s neck as reference. The horse needs to keep his head straight and upright in the gallop which is made possible by maintaining the reins straight right from the mouth of the horse to your elbows. This will prevent the horse from dropping his head to the knees.
If the horse loses control, you should not pull on the reins as this will only force the horse to pull against the reins with more force. You should begin with a gentle pull on one rein, to initiate circling as this will gradually help in reducing the speed of the horse.
You can now resume the canter and then the gallop.