From the video:

Here is the way I suggest doing the dumbbell shrug.
1) Grab the dumbbells with your palms facing in
2) let the weights hang at your side
3) keep your arms straight, dont bend the elbow
4) put your shoulders back, try to squeeze your shoulder blades together
5) go up and down slowly, as far up and far down as you can
6) dont roll the shoulders!!!!