Neck bridging is by far the best neck exercise there is. You utilize your whole body in a dynamic manner, and use your neck to work against resistance, while maintaining stability. This exercise has proven greatly beneficial for me, both in terms of neck size and strength. I would recommend using your hands to balance yourself if you are a beginner, and once your neck grows stronger, you will be able to balance solely on your head. The technique is to rock back and forth, aiming to go as far back without hurting yourself. Once you become more advanced, you can start rotating and moving at different angles.
