To develop the middle and upper pectoral muscles. You can vary the angle of the incline bench from almost flat to almost upright; the more upright the bench, the more you work the deltoids.
Take a dumbbell in each hand and lie back on an incline bench with each dumbbell resting on your upper thighs. Kick and swing the dumbbells up so that they are at shoulder height, palms facing forward. Simultaneously pushing them straight up overhead. Next, lock out your arms over your head. After this, bring the dumbbells back down to your chest, pause for a second with the dumbbells on your chest. Keep the weights under control throughout the entire movement. Then press it back up to the starting position.
You can vary the way your hands are positioned also by starting them off palms facing forward and twisting them as you lift up where the palms would be then facing each other. At the top of the movement it is important to really squeeze the pectoral muscles as much as possible. To help with the squeeze picture yourself bringing your upper back or lats slightly off of the bench reaching for something. This will enable you to get the most out of the squeeze.
Like said before this lift can have several variations on the incline bench as to where you set the incline. the steeper the incline the more stress on you deltoids you will face. You can vary it from workout to workout or set to set.