Most people roll their shoulders, which means they bring them forward and then up. A shrug should be straight up — think of driving your shoulders toward your ears in a vertical line, not a rotation. Stand facing the cable machine or with handles at your sides, arms straight but elbows slightly bent. Shrug your shoulders up hard and squeeze, then lower. Your arms do minimal work; it is all shoulder. Keep your chest upright and avoid twisting. The cable's constant tension means you cannot rest at the top like you might with a barbell. Maintain tension throughout.