I talked about bucking yesterday - and why you might not want your horse to do it.
So, how do we stop them?
Bucking is caused by one of four things:
2. Asking a horse to do something it is not physically or mentally ready for.
3. High spirits.
4. The horse becoming "angry" at the rider.
The most common cause of bucking in an otherwise trained horse is pain or discomfort from ill-fitting tack or from back soreness (modern horsemen often retain the services of an equine chiropractor). Horses may also buck because they got bitten by a fly in a particularly sensitive spot. Not tightening a back cinch the correct amount can also cause bucking.
So, obviously, you want to avoid all of these scenarios.
On the second thing - the most common time you see this is when a horse is saddled for the first time and again when mounted. Cowboys used to "break" a horse by getting on and letting it buck until it realized it wasn't getting it anywhere - which is where bronc riding comes from. (This technique would probably be used by any culture with a high demand for mounts and limited time to get them ready - it works, but is generally considered "harsh" by modern standards). If time is taken to get the horse used to tack and weight, they're less likely to buck.
Obviously, a horse that's showing high spirits and wants to play just needs to be worked harder...and gently reminded that it's rude to buck while somebody's sitting on you. I think some of them just forget.
The horse getting mad with you is harder to avoid. Sometimes you just have to get into it with a horse and some of them will use bucking you off as a weapon. Others will buck when you hit them with a whip, and I suspect most that do this have learned that gets most people to back down.
So, what do you do if the horse actually bucks? The answer is to make them go forward. You use legs and seat to really drive the animal forward. A horse has to slow down or even stop to be able to buck.
The horse also has to be able to get its head down. English riders will sometimes use a technique called "bridging the reins" on a horse that is bucking repeatedly. The reins are crossed between the hands and then braced against the withers. This both stops the horse from getting its head as far down and helps the rider stay on.
Habitual bucking tends to require that a horse be sent back to a trainer.