Knee bend is important. If you bend too much at the waist, you'll find yourself off-balance at the foul line.
Eliminating the muscle from your swing is a huge help for balance as well. It is much easier to remain in a fixed, balanced position when you're not pulling the ball down from the top of the swing, trying to start a lawnmower at the bottom of the swing, and rearing up at the line.
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J.J. "Waterola Kid" Anderson, the bLowling King : Kill the back row