Dont roll the shoulders. Like Louden said, it can pinch nervers, or fuck with your rotator cuff. Also, use dumbells, it lets you get better range of motion, which is key for trap development (kinda like full ROM when doin calves).
Straight up and down. Hold it for a 1-2 count at the top of the motion. Start with a warmup set or two, then go heavy, then finish with a set or two of higher reps.