Stand with your feet shoulder-width apart, holding a dumbbell with both hands. Start with the weight at one side of your body, next to your hip. Engage your core, and lift the weight diagonally across your body, ending above your opposite shoulder. Keep your arms straight, and rotate your torso as you lift the weight. Slowly lower the weight back to the starting position. Perform three sets of 12 to 15 reps per side.