I agree with the suggestions. If you can sorta anticipate when they are going to buck; shorten your reins up and bring her head up as best as you can, sit down deep in your saddle and drive her/him forward with your seat and legs. I was once told that the best gait to ride when they are bucking is a trot, just trot them through it. If it continues I would get a professional in to see what the problem is. Buckings no fun! I have been chucked on to some very poorly broken in horses!
All I pay my psychiatrist is the cost of feed and hay, and he'll listen to me any day. ~Author Unknown