I will try and explain the process I go through to get my horses trained for WP.
First I start off by getting control of thier body movement. Like steering, two handed and one, turn on the forehand, turn on the haunches, side pass, walk, trot, canter. I want my horses to understand what all the gaits are and be comfortable in them.
I then work at getting my horse balanced and working from behind. I work on getting collection and ask them to frame and carry themselves properly. Once they have gotten that down then I will ask them to slow down their trot into a jog. I want to find what is right for my horse. If I'm working with my mom's arabian then he is going to have a little more spring in his step then my morgan, it's just who they are and that will never change.
I work a lot on transitions between walk/jog, stop/jog, jog/walk, jog/stop. When I'm asking my horse to speed up from the walk or stop into the jog I will first ask them to frame and soften before asking for the change in pace.
Once I have the jog where I want it then I will work at getting a lope. There are many ways to get a nice WP lope and you have to find what works for your horse. One way is to repeat what I've done with the jog but asking for a lope. Start by using circles of every size. Ask for the canter in a good frame, then ask them to slow down bit by bit. Keep them framed so they don't get all strung out. If they lose thier frame/balance they will not be able to maintain a slow lope without breaking gait. Work on moving them in and out of the circle making it bigger and smaller. Once they have that down the I start working on transitions. Again I ask them to frame before asking for the lope. I do jog/lope, walk/lope, stop/lope, lope/jog, lope/walk, and lope/stop.
The other way I have gotten the slower lope is to work out on the trails. I will ask my horse to jog for a fair distance, walk, then lope for a fair distance. I don't stop the lope until after they are looking to stop, I then push them a little longer (not much) and then ask for the jog for a little and then the walk to give them a break. Once they get thier wind back then we repeat the process. Eventually they will just go straight into a WP lope right away every time because they want to conserve thier energy. For this process I still ask them to frame and soften while working.
Once I have the gaits down pat then I fine tune thier neck reining (I work on this the whole process but now I focus on it). I want them to neck rein with very little effort on my part.
Sorry it's so long, but that's what I do and it has worked for all the horses I've trained, with some differences depending on the horse.