Exercises don't get much simpler than the dumbbell bench press: You lie down and press two dumbbells straight up off your chest. Still, you'd be surprised how many guys screw this one up. In their desire to get fancy and work the chest even harder, they tend to rotate their palms inward as they press the weights up (so they face each other in the top position). While you might think this rotation activates the pecs more, it actually allows them to relax. The method is wrong, but the concept is correct-turning your wrists really can build a bigger chest. You just need to rotate them in the right direction.
HOW TO DO IT
Grab two dumbbells and lie against a bench as you would for a normal bench press. Start in the bottom position with your palms facing each other so the handles of the dumbbells are parallel to your body . Now press the weights up, turning your palms outward so that your thumbs face each other as you lock your arms out (you'll end up in the same up position as in a regular dumbbell bench press) . That's one rep. Perform three to four sets of six reps, resting 90 seconds between sets. For best results, slow down your lifting speed: Take three seconds to lower the weights, and then pause in the bottom position for one second. From there, take one second to press the weights up (beginning the next rep).
Due to the way the muscle fibers in your pecs are arranged, you activate the chest a lot harder turning your palms away from you when you press as opposed to pressing with your wrists in one position (or rotating them the other way, which has less benefit). The added bit of stimulation can make this exercise the turning point in any chest-building routine.