Get your upper back off the top of the bench. This allows the scapula to move with more range of motion, allowing the pecs to get into a more lengthened state.
Keep your palms forward and bring the dumbbells back toward your ears, not down to the side of the body. This also puts the pecs into a deeper stretch.
Use only a slight bend in the elbows. Most people get way too much fixed elbow flexion with flyes, turning into more of a half press/half-flye type of movement.
Want to build great abs? Forget sit-ups. Want great biceps? Forget all those curls. Want a great chest? Forget the bench press. According to Chad, isolation movements are a waste of time. He's either nuts or a great visionary.
This exercise teaches you to hold the shoulder girdle rigid to avoid strength leaks in pressing lifts. It strengthens the front delts, rotator cuff, and even the lats.