Bodybuilders and athletes know that neck is a very dangerous muscle to train. This is mainly because it can be seriously and quite easily injured. This is why it’s usually safer to let it grow at its own pace. However, there are some who persist on training it, so for them there is a safe way to train it. It is called - neck curls. You lay down on a flat bench, with your head hanging slightly off the bench. Take a weight plate and place it on your forehead. Now, making certain your neck is relaxed and entirely extended downwards, slowly curl your neck upwards, almost like you’re trying to touch your chin to your upper pectorals. Then slowly lower it down. Make certain you aren’t lifting off the bench.
The key to this exercise is to use a moderate weight. Don’t start by throwing on 25pds. Start off just doing them without any weight, then slowly adding. Once you are using a 45pd plate, you are pretty much stuck at that weight. You may want to try putting a dumbbell against your head and doing the movement, but it is not recommended due to too much stress. And remember, neck injuries are quite serious and will hamper your training.