I think someone else posted a similar question recently, so you might want to try a search and see whats been said before ?
But in general, neck reining comes when you have already established basic cues i.e. it is a result of training, and not something I would want to do in isolation.
My mare is in a snaffle, and I ride with both hands, and I would start to teach neck reining as part of the transition to a curb. The build up is being able to use legs and weight to influence movement, and teaching the horse to yield to pressure. Gradually introduce more indirect rein contact, and that will build into neck reining.
But as I said, I think this has been answered before so have a look around ! (Who knows what other interesting info you'll find