Here's a good column from Larry Dierker about J.A. Happ and what he's doing wrong.
If I were managing a team that was facing him, I would instruct my hitters not to swing at anything but a fastball right down the middle until he threw at least one strike. That's what the Marlins did and it worked pretty well...
...So, how do you avoid walking so many batters if you don't have good control? You stop throwing a wide variety of pitches and concentrate on two or three.