Stand holding a pair of dumbbells at your sides, palms inward facing each other. Pull shoulders up and forward, pause return, repeat.
Proper technique is demonstrated when the head is focused forward and the upper chest is held high. Now, the spine is properly aligned, the scapulae are retracted slightly, the shoulders are braced and the upper trapeziums will be in perfect position to forcefully elevate the shoulders — building big traps and preventing injury.