whats the best way to do shoulder shrugs?
 

I can't get on with these doing heavy 8 rep sets I dropped the weight and do 16 quicker it seems to work a lot better, is this right?

fast up slow down is the best way to build mass and strength. more reps less weight will lean the muscle out not make it bigger so it all depends on your personal goal

depends on your goals. if you want to gain size... more weight, less reps.

With these muscles you should be more concerned with the quality of the lifting movement. Keep it slow, otherwise you'll get a bounce and that's not going to help improve your body too much. So, do lighter weights, do them slowly, you'll find that you can only do about half as many reps, but it will be very effective.