There's this thing called 'heeding' that I do with my four year old stallion, and it works really well- it sounds fancy, but really, it's just this- when you take them out, you walk them. You keep walking them, when they do something bad, or misbehave, don't freak out, don't change what you're doing- keep walking, making them turn in circles, back up, turn away from you, etc. The point is to not react to anything but when he does well, so that he feels that he's overreacting and will eventually calm and focus on his work. It works well for my stallion.
I also have what I call a 'danger word', which for me is 'quit'. While the heeding thing is more of a neutral type of work with no real negative reinforcement, and just a pat and a word of praise when he does well, this is a negative association- when he does something bad, when you discipline him, say the word, and he will eventually associate the two. This also works for my stud- when he gets excited, I just say 'quit!' and he stops what he's doing and looks at me like, 'What now, mom?' He has his moments, but he's much more well-behaved than when I got him, and not at all as crazy as people were convinced he was (without evidence) JUST because he was a stallion.