Here is a simple exercise you can do for the trapezius muscle. Despite popular belief, the trapezius is not part of the shoulders. It is actually a back muscle that allows the shoulders to move in different directions (e.g. elevating and lowering the shoulders).

Begin with your feet just a few inches apart. Grasp a dumbbell in each hand. Ensure your posture is properly maintained. Your stomach should be sucked in. Your back and head should be straight. Next, slowly elevate your shoulder blades, then return to the starting position. Never let the shoulders drop [due to gravity] on the way down. Be sure to control the momentum at all times.