I start them neck reining in the snaffle only
after they are solid on left and right with direct reining and soft on the bit. I will work in squares on them. Walk them for a minute, lay the right rein on their neck then a moment later, direct rein with the left rein until you get a turn then release all pressure and let them walk. Then do the same thing again and again and again. Then move up to the trot and start over, then the lope.
Here is a sorta mediocre video showing what I just described. YouTube - Training Tips: Neck Reining and Pivoting, part 1, eXtension