Keep your back as straight as possible and bend over at the waist lowering the dumbbell over the top of you feet

Your knees should be kept stationary during the movement.Focus on the stretch in your hamstrings, and continue to lower the dumbbell down as far as your hamstrings will let you comfortably.Now engage the hamstrings and begin to raise the dumbbell straight back up

Your eyes should be facing up and your shoulders back

Squeeze up through the glutes and hamstrings until you're standing straight up.