The best way to prevent bucking is just to be consistent and fair with your horse and to properly prepare them for what you expect them to do. Don't push them to do more than they are ready for and capable of. In my experience, a young horse (that isn't already a habitual bucker) is most often prone to buck on either the 3rd ride or just going in to the 2nd week of work.
Just make sure that you give them adequate time under saddle before asking for anything too strenuous; keep them at a walk for a while and then at a trot for a while before asking for the lope, let them warm up and relax for the first few minutes of a ride. To just jump on a fresh greenie and lope them right off is asking
for them to throw an "I'm feeling good" buck.
In the event that you do end up with one that bucks, the quickest way to stop them is with the one-rein stop. Don't ever use both reins because that gives them something to brace against and buck harder (think saddle broncs at the rodeo, that's what they use the bronc halter for). If they are supple to lateral bending, then you can get their neck bent and their hindquarters disengaged and many will stop bucking pretty quickly after they because they get off balance. Even if they keep bucking a little, if they are bent, that takes away much of their power and makes it easier to stick with them.