The KING for Traps is Deadlifts. These babies will make them huge. Stand before a loaded weight. Squat al the way down, take the bar using a little closer that shoulder width grip. Take your normal stance feet apart. As you lift the weight, drop your ass to the ground, lift with your legs as the weight starts climbing past you knees it is all back. Slightly hyperextend. This allow you to squeeze the Camels together, those traps muscles viewed from the back. This is by far the very best. Shrugs are ok but used more for extra isolation. More on that another time. Good luck. The better the technique the bigger you get, otherwise you are just wasting energy. It is not what you do but how you do it!