Lay on a flat bench, dumbbells in hand. Form a straight line with your arms through your shoulders, maintaining a slight bent in your arm, palms facing up. Bring the weights up by squeezing your chest, exhale, bring the weight down, inhale.
As with other exercises, let’s first focus on what will hurt you. Going too far down is the most common way. Your upper arms should never go more than 10 degrees lower from making a straight line through your shoulders. Doing this exercise too quickly is another way to get hurt. Unless you want to tear your pecs, control the entire motion of the exercise. Do not use heavy weights. This doesn't mean that you shouldn't go heavier as you build your chest, but don't go heavy and sacrifice form. Maintain only a slight bent at your elbows. The greater the bent, the more this exercise is like a dumbbell press and not less like a dumbbell fly.