Start by looping the theraband at a point above your head and to the side of your body.
On the same side, loop the top of the power band over your shoulder, it should be resting over your deltoid muscle and not above your shoulder. Step on the other end of the power band to apply a downward pull. With your opposite hand, hold gently on to the power band around the middle to stop it from slipping out of position. Then slowly allow your shoulder to move into abduction / moving away from the side of your body. Make sure that this movement is controlled and you do not allow your upper trap to switch on.