I have barrel raced for 10 years now and have had lots of experience training barrel horses. The best way to start a barrel horse is to make sure that the horse understands how to bend and walk, trot, and lope circles. Walking the horse around the pattern after the horse knows how to circle correctly. Getting the horse patterned is the most important part of starting a barrel horse. Make sure you walk, trot, and lope him on the straightest lines to each barrel. If your horse fights you, you may want to consider putting a tie down on. Tie downs are not "mean" to the horse. Most barrel horses use a tie down to brace themselves when they are really running and digging. It also prevents the horse from throwing his head so high that he hits you in the face. I have had that happen, and its not fun or pretty! Hope this helps and good luck! Post pictures of you barrel racing when you get him going!
I apologize but I don't find this to be very good advice.
I've ridden several horses who know how to bend and flex but do not know how to move their body part independently. Causing them to be prone to dropping shoulders and bowing out when they anticipate the turn ,while the rider desperately struggles to maintain their composure by pulling their head away from the barrel and ripping it back to make the turn.
A barrel horse MUST have SHOULDER control if nothing else. I'd rather have control of a horses shoulder while barrel racing than just have control of his face.
Tiedowns have their place but it isnt where you stated.
"If your horse fights you, you may want to consider putting a tie down on."
This was on the verge of disturbing to me. If a horse fights you...its a dead give away that something is lost in the translation and its time to take a few steps back and re-check your training OFF the pattern. If the problem doesnt get resolved through training, then its a possibility that the problem is physical.
"It also prevents the horse from throwing his head so high that he hits you in the face."
This action screams I HAVE A PROBLEM HERE! and a tie down would be a foolish decision.
Barrel training starts off the pattern. CONTROL is everything. You need a solid base before even touching a barrel pattern. Meaning a horse that will whoa (by shifting your weight and still staying soft in the face),Extend and collect without throwing the head or gapping the mouth, counter arc @ walk trot and lope, pivot smoothly, and roll back calmly.
Once these maneuvers are embeded in the brain, slowly move onto the pattern. Slow work differs from horse to horse. Some horses like to drop into a barrel and others like to be loopy.