1) Make sure diet, sleep, life style choices are optimal.
2) Dead lift and variations with challenging but not crippling weight using good form.
3) Know the function of a muscle you're training or risk stumbling in the dark.
4) Flex the muscles in question to increase mmc.
My upper traps were never a strong point. They're still not where I want them but that's the challenge, isn't it...? And as a natty recently starting a 55-60 hour job really didn't help matters.
This year, I took to heart my former Coach's advice re: deadlifts and started doing them consistently. The intention was NOT to build upper traps but fill in gaps in strength and overall health.
The side benefit is the upper traps did start growing.
So you have three posts so far in which the writers have photographic evidence - VERY VERY important when listening to advice on bodybuilding - that they know a thing or two on the subject. And all three agree on pulling heavy things from the floor.
But here's the disclaimer: heavy weight does NOT mean crippling weight; it means weight that is challenging TO YOU.
I've seen guys trying to hit max singles every time they deadlift. This is a high-risk approach with potentially severe consequences. The weight room and meat head forums are littered with guys who bit off more than they can chew and suffered permanent injuries. This is the single most important take-away I got from my Coach.
I stated this in the Conditioning subforum a while back http://tnation.T-Nation.com/free_online_forum/sports_body_training_performance_bodybuilding_conditioning/push_ups_pull_ups_squats_work_all_muscle_groups and it's worth repeating: 1) learn proper form; 2) do different variations on the deadlift; 3)use moderate reps and always walk away with something left in the tank.
This might be hard to hear but if, after two years, you haven't accomplished much, then I doubt your diet was optimal. I also doubt you were performing all those shrug variations in an optimal manner.
The upper traps don't just elevate - they also retract. Now let this knowledge bomb sink in. I've lost count the number of idiots just load up the smith, strap up, and mindlessly shrug up and down. Unless they're gifted or using, I'm convinced this method is garbage and they'll be lucky if they don't injure a nerve at their cervical spine.
Another thing no one mentioned is the importance of flexing the targeted muscles. This is an old-school bodybuilding technique that really helps you to be in tune with the muscles in question. Get in front of the mirror and practice the most-muscular pose until you can flex those muscles at will.
There are also some more advanced techniques but human nature being what it is, I fear neophytes will jump straight to that and ignore the fundamentals.