Typically, when the 9ball is going in on the break a lot, it's because the balls right behind it are not frozen to the 9ball. As a rule, you should always try to freeze-up the balls as well as you can. Your opponent will be checking to see if the front three balls are frozen. Your job as racker is to make sure the 9ball and the two balls behind it are frozen. This should keep the 9ball in place for the majority of your racks.
A good practice is to rotate the balls behind the 9ball every time you rack. It's a simple routine to get into and will help freeze up the balls.