With DB's at your side, keep the shoulder blades down and back and out of your ears. Keep the trunk in the upright Iso-Ab position.
Take a step to the side with the trailing leg staying extended, Drive the hips back, keeping your feet, knees, and hips aligned pointing forward and not out to the side. You should feel the glutes and hamstrings of the side lunge leg, adductor of the straight trailing leg and the upperback and midsection keeping you upright.
As you push off back to standing with the lunge leg, curl the DB's to your shoulder, and repeat with the other side.