You will have the most success, according to Johnny Bergeson, if your horse is mouthy, likes to touch everything, and is curious. If he is not, he will not respond all that well to tricks.
Before you teach the horse to lie down, you will have more tricks to work with if you teach him to bow. From the bow, you can push him over to lie down, but if you start with the lie down, it is hard to get him to stop halfway to get the bow. On the other hand, if you bow first, then later, lie down, you can get both.
To teach your horse to bow, have a treat in your left hand, pick up his left foot in your right hand and coax him "down" a bit to take the treat. Every day, you coax him a little lower until you can set his knee on the ground. This is easier said than done. You will have some bad days when he says, "Not today, Mom, ain't gonna do it." Just keep at it. It takes work, patience, and a horse that wants to do tricks. Reward the slightest movement lower.