Exrx:

Shoulder Shrugs Errors (shoulder rolls)

Shoulder Shrugs ErrorsRolling (horizontal movement) is nonsensical
Weight moves perpendicular to gravity
In an upright posture, the upper traps and middle traps resist weights against gravity (downward force) as they elevate the scapula
see correct form
Although it is true the middle and lower trapezius can also retract the scapula on a continuum of planes
they resist such a load retracting against a resistance on a transverse plane during general back exercises
or by upward rotation on a frontal plane during shoulder exercises
Bottom line: It's only necessary to raise and lower the shoulders during shrugs. The lower and middle trapezius will be exercised during other basic exercises
Also see ROM Criteria

Also: http://www.aworkoutroutine.com/rolling-shoulders-during-shrugs/

Basically, it's as it sounds. Stand up, put your hands in your pockets and try moving your shoulder (1) in a circle (2) straight up and down.