The best thing for a green horse is lots of riding and many sweaty saddle blankets. To begin with ride him in a true loose ring snaffle bit using both hands on the reins. Plow rein or direct rein him to start with. When moving on to neck reining it can be confusing to the horse. If you study the physics of neck reining you can see that the horse's nose is tipped in the opposite direction of the neck rein. That is one reason the importance of using leg cues comes into play. Best Wishes for a successful experience.