As with most exercises, keep the rep range long (dont stop half way down and raise the dumbbells), control the dumbbells, and concentrate on stretch and contraction.
Instructions
Set up for the palms in decline dumbbell bench press by setting a pair of dumbbells at the end of a decline 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, securing your feet in the padding.
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 the dumbbells straight up above your chest with your palms facing in. This is the starting position for the movement.
Slowly lower the dumbbells down as far as comfortable possible (the handles should be about level with your chest).
Pause, and then contract the chest and push the dumbbells back up.
Do not lock your elbows out, and then repeat for desired reps.