Lets see (was a few years ago now) if I remember exactly what I did with Dizzy.
Started with low table and had the contact part of the dogwalk on it (top on table, contact part on floor). Dog on lead (harness is good as it stays central on the back). Plate with food on, about 1 foot away from contact (this depends on size of dog).
Dog knows food is on plate and can see it. Give command and allow dog to descend and stop in correct position (thats why dog is on lead and can't get it wrong - hopefully). Once in place reinforce word and position - I use the word 'feet', so it was 'feet, good feet, good feet' etc etc. Continue with exercise until dog is happy with word and position, and that you can allow the dog to complete exercise without your intervention with lead pressure (this will be done over several training sessions and not all at once).
Don't move on till you are happy that the dog knows what is expected of him.
I then progressed to a low dog walk (short tressels). Held dog in front of dogwalk and gave command (the up and along a dogwalk doesn't really need to be taught as they tend to just do it). When happy you can transfer skill to full height dogwalk. It is always helpful to have someone to pick up food if your dog has a tendancy to run round to food. Dogs are clever and soon learn that they have to do required exercise before treat is allowed. I was lucky and had no problems - Dizzy was quite happy to go over dogwalk to get treat.
With my young dog I started as a pup by placing her on the end with the plate and food and reinforcing the position and releasing to her toy.
This progressed to moving her back a foot and bringing her into position, then 2 feet etc. She thought it was great, food then ball, food then ball and loved doing it.
Obviously this method works just as well to a target and clicker, and you keep the motivation.
I am very happy with this way of training as it has worked for mine. But there are many ways to train contacts and you see lots of dogs are shows which have fast and accurate contacts, which may have been trained differently. Maybe at a show, speak to someone you have watched in the ring and liked their dog's contacts, and see what they did, they may be more than happy to share their words of wisdoms