Instructions
Practice maintaining a steady seat while riding at all gaits in a controlled environment, such as an enclosed pasture or arena. Focus on sitting deeply in the saddle and maintaining correct riding posture with your heels pointing toward the ground and your back straight. Keep your hips as loose as possible and allow them to move with the horse.
Take horseback riding lessons from a certified instructor who is qualified to pinpoint areas where you may be having problems. The instructor can give you individualized coaching to improve your seat.
Lean forward slightly and stand up in the stirrups when galloping. Put your weight on your heels, keeping your heels down. You only want to raise your buttocks off the saddle by an inch or so --- just enough to stabilize the bouncing and avoid causing the horse potential back pain.
How to Keep From Bouncing on a Saddle When a Horse Is at Gallop Speed
Becoming a skilled horseback rider requires a lot of patience and practice. The faster a horse is moving, the rougher its gait. An inexperienced rider may have difficulty maintaining a smooth ride on a galloping horse. The four-beat gallop requires a certain amount of experience, but there are ways for inexperienced riders to reduce bouncing.