Two things, a good bit and clear cues.
Honestly I've found most horses figure out how to neck rein rather quickly with a short shanked, ported or mullened, curb bit. I use a bumper sweetwater bit:
If you want to stick with a snaffle then essentially you're teaching the horse a pre-cue, the rein touches the horse's neck, if they don't turn you direct rein them. Do this enough and eventually they'll turn with just the pre-cue, before you need to pull. But that's essentially what a curb bit does on it's own.
What happens with a curb bit while a horse is learning - you neck rein left, your right rein is shortened, this pulls the right shank up and takes the pressure off the right bar - pushing onto the right cheek, which pushes pressure down on the left bar. This provides a number of very clear signals for a horse to follow when you neck rein, the horse will also learn the pre-cue of the rein touching the neck before the contact on the bit happens.
So if the horse gives well to direct reining it could be as simple as changing to a good quality, gentle, curb bit. But if you want to stick with the snaffle your best bet is to train the pre-cue.
Good luck - have fun!
ETA: Also - welcome to the forum!! We love pony pics here so feel free to post up
I do as PunksTank does and just wanted to add that when I cue the direct rein, after laying the indirect rein on the horse's neck, I really release quickly. I want to reward the tiniest turn of the head when the horse moves it in the desired direction. I build from there, gradually eliminating the direct rein.
If your horse turns off your leg, then he will neck rein. It's more about the using LEG first, then adding a slight cue with the hand.
Adding to this - if you are teaching your horse to neck rein and he already knows leg pressure, this will assist in the teaching process. Touch rein to neck first, if no response, then use leg, if no response, then bump inside rein. That's how I've always done it. Obviously once you really get going and the horse gets the hang of neckreining, you can steer 90% off your leg and just refine with the reins. And I always use an unjointed short shanked curb like was posted earlier, except mine was just a low ported "grazing" type bit.
^ A friend of mine was ridinng my horse yesterday, she had only ridden him once in her life. She asked me how to neck rein him (she's a hunt seat rider), so I told her to lift her hand up and apply outside leg, and he went right around for her. Next thing you know she's jogging through three trot poles and doing tight turns around the end of the pole to jog through the other side; just by a little leg and a lift of her hand.
As far as bits go, all of mine are ported but have swivel shanks....except one bit which I show WP with. It is solid but in the mouthpiece and the shanks. I find the moveable shanks much better for teaching "neck" reining than one with a solid shank.
Dun - that's very interesting what you say about swivel shanks - i'm not arguing, just curious, what Makes swivel shanks better? Do you have a picture of a bit the style your explaining? Thanks! I just like to learn about bits and styles and why people like different types :) Posted via Mobile Device
^ I will post some when I get home. The reason I like swivel shanks is because they have both independent action AND solid action. You can "pick up" one side of the horse's mouth and not the other or both. With a solid bit all the way through you don't have the availability.