1. Take a treat in one hand and tempt the horses head down. Say "bow" as the head goes down. Repeat.
2. Pick up the left front hoof as if to pick it out and again tempt your horses head down with a treat as you say "bow". Repeat.
3. Pick up the leg with your left hand and put the hand with the treat in it inbetween the front legs. Tempt the head and say bow. Repeat.
4. Repeat step 4 until you can gently lay the leg down on the ground. The other front leg may quiver but keep practicing until he builds up the muscles.