So far I've trained one horse to jump... I will eventually teach my mare but for right now I will tell you what I know (I'm an amateur trainer).
How is he lunging over ground poles at a walk? Trot? Canter? This is the first step. Start with one pole at a time, about 9ft apart for walk/canter and about 4ft apart for trot. Once your horse gains confidence add a pole and so on. After you have about 4 -6 poles on the ground, you can add your first jump. Start with the pole on the ground, then raise it on one end (about 6inches-1ft), if he goes over that fine then add another cross rail. Keep doing this until he gains confidence. The most I would jump for the first week of two is 2ft. Then once he builds the muscle and confidence you can slowly work your way up :) This is what I did, we eventually made it to 4 1/2 ft!
I wish you the best of luck!