I start teaching "go" from the ground up...the cues stay the same...and the pressure 'increases' as the horse 'lacks' response.
I click first...if no response, I will tap the air near the horse's hip (undersaddle, this will be a light squeeze with my calves), if still no response, I tap the hip with increasing intesity until the horse responds, and AS SOON as he responds, I release.
Undersaddle, I lighten my seat, loosen my reins, and click...if no response, I then squeeze with calves, and if still no response I spank with crop or mecate. Always, always start out as soft as possible, not hard...you want the horse to respond to light pressure, not have to rely on hard pressure. Reward the slightest effort in the beggining and then gradually ask for more and more. Horses learn from the release, not the pressure that's put on them.
I also agree with christopher...do not get on a colt until he knows lateral pressure and is very soft laterally...this is your lifeline if he decides to do anything goofy in your first couple of rides, as you will be able to disengage that hind quarter!!! I always do alot of transitions from the first ride on...don't just get on and walk, get those feet moving from the get go; it can be very helpful to have another person to do the 'driving' as well.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."