Using both legs makes the move more functional; it mimics how you move in everyday.
Hold a pair of dumbbells at arm's length next to your sides, palms facing in. Step forward with your right leg and slowly lower your body until your front knee bends to 90 degrees. Pause, rise up and step back to return to starting position. (Note: Keep your back straight and avoid leaning forward with each step.) Repeat with left leg. Alternate legs for 15 reps.