Hehe I just started helping my little sister teach my horse to bow and he gets it but he is so suborn lol I also have thought about teaching him to rear on command but he is getting on in age and I don't want to push him too much. You could also teach a mini to give kisses and smile. Most horses are wonderfully treat motivated only thing is you have to be careful they don't start getting pushy about treats. Tricks are a GREAT way to help keep a horses mind sharp and working!
Look on you tube there are alot of videos that can sometimes help or give you other ideas how to train there is never just one way to do it!
I taught my gelding to "say yes" and he nods when I ask him if he is bad..which now he does like crazy..expecially at feeding time...and he knows how to "be ashamed of himself", it was really easy to teach..Start standing in front of him and have a treat in one hand, teach him to duck his head under your arm and have a treat behind your back to give him when he does..it's just a cute easy trick..
How far are you wantin to go with it? I've taught horses to lie down, bow, stand on a pedestal, give kisses, and hold a whip in their mouth and rear on command.. It's really not that complicated once you understand how the horse thinks.
PM me I'd be glad to help :)