As a general rule you should always work the weakest side of your chest first. For most people this will be the left side.
You can use this exercise to bring up weaker areas of the chest.
Keep the rep timing slow and control the weight throughout the set.
Instructions
The alternate dumbbell bench press is a great exercise for increasing chest, shoulder and tricep size. Set up for the exercise by setting a pair of dumbbells at the end of a flat bench.
Pick up the dumbbells off the floor using a neutral grip (palms facing in), position the ends of the dumbbells on your thighs, and sit down on the bench.
To get in position you need to rock back pushing the dumbbells back with your thighs and only slightly bending at the elbows. Now you should be in position to start the set, laying back on the bench holding them dumbbells straight up above your chest. This is the starting position for the movement.
Slowly lower the left dumbbell down as far as comfortably possible while holding the right dumbbell in place.
Pause, and then contract the chest to move the dumbbell back to the starting position.
Repeat on the right arm. This is one rep, now repeat for desired reps.
Once you have finished the set, DO NOT DROP THE DUMBBELLS! Twist the dumbbells around to neutral (palms facing each other), bring your knees up so the ends of the dumbbells are touching your thighs, and then use the weight of the dumbbells to rock back to a seated position.