traps are a tricky muscle, a lot of times a guy doesn't know whether to work em' with shoulders or with back, I actually work mine with shoulders, mainly because my back workouts a so intense that usually I don't have a lot left to give my traps on back day and because my traps seem more stimulated on shoulder day than on back, i do close grip shrugs followd by heavy upright rows, if you bend forward slightly on your upright rows your traps will take over, so remember to focus on your traps and not your delts, also if you have a tbar get on that and with your arms full extended use just your traps to lift the weight, basically a shrug that isolates the traps very well. I have noticed great gains in the overall mass of my traps with these exercises.