My 2 cents worth.
Start out with direct reining, until he responds well to the leg cues, then graduate to neck reining. He will begin to associate the rein cues with the cues from the legs. In order to get him to respond quickly and willingly to the leg cues, though, you may need spurs. I give a leg pressure with the calf once, twice, then a touch with the spur. Next comes a pretty good jab with the spur, and I'll keep bumping him with it until he responds. He learns pretty quick to respond to the first cue. An added benefit to this method is that you control most of his movements with the legs and his neck reining becomes almost imperceptible. If you're into shows, this gets points.
The leg cues I give are pretty simple: In front of the cinch to move the front end, on the cinch to side-pass, behind the cinch to move the rear, pushing in the direction I want him to go with the outside leg. I put a little pressure in the inside stirrup, as if leaning into the turn as well. The harder I give the cue, the tighter the turn I want. I expect the horse to continue to respond to the cue until I stop giving it. The legs control the body, the reins control the head.
There's more to it than this simple explanation, but you get the point. Start out just being satisfied with his effort to figure out what you want and reward him for the slightest movement in the right direction. One step, then ask for two, then keep going. Take your time with it.
If you're going to use spurs, though, learn how to use them. They are training tools, not weapons.