Position your legs securely in the padding of the decline bench and lay back slowly with a dumbbell in each hand (palms facing each other) resting atop of your thighs.
Extend your arms out above (palms still facing each other).
With elbows slightly bent, lower the weights in a semicircular motion to your sides.
You should aim for a stretch in the chest musculature.
Don't lower farther than your standard range-of-motion or at/below your chest.
At the bottom position, return back to the top, on the same path as the eccentric, as you squeeze your chest to initiate the concentric portion of the exercise.
*Tips*
The arms should remain slightly bent throughout the movement. The arms are a lever between the chest and the dumbbell.
The focus of this exercise should be on the stretching and contraction of the chest musculature and should be done at a slow pace.
Going too heavy on weight can ruin the stretch and defeat the purpose of the exercise.