Use a neck machine.
Do bridging on the floor (like a football player or wrestler.)
Do shoulder shrugs, straight up and straight down, as they should be properly done (without rolling).
Don't do stupid movements like putting a weight plate on your forehead.
Many guys overdevelop their neck and traps. Unless you're very thick and wide through your upper body, doing so will wreck your upper body symmetry.
Before you bust balls on your neck, take a good look at your symmetry and decide if it's what's right for the best look. Sagi Kalev, a personal friend of mine, one of my trainers, and the man who has appeared on Muscle and Fitness more than any other person in the world, only weighs about 205, but, spends lots of time on his symmetry. Sagi had me back off my traps and neck. See him at: http://www.sagikalev.com. Nearly everyone agrees that Sagi is gorgeous.
It's all about how you package it. If you have great abs, but, otherwise look like you come from the middle of a dessert that's not a good look, or, if you're very fat and only look "big" in winter clothes, that's the other extreme. If you have low esteem, run pictureless, or are icky of personality, but, have a great bod, what good are you?
All good things in balance generally works best...even your NECK.