Perhaps you would like to show your miniature horse in halter classes. Let's say your horse already knows how to set up, perk his/her ears forward, and stand still, but he/she is overweight, not very muscular, or just needs some fitness.
Start the conditioning out easy. I started by walking my horse up and down hills. She got more confident, so we started trotting up and down those hills. We did this for a little over a month, and her physical and mental fitness peaked.
My mare was now ready to start being round-penned. We were boarding at the time, and I simply made her run around in the round pen. The round pen caused her to go in circles, so her chest got stronger, and her back legs strengthened right out.
Since she was round penning nicely, I decided to train her to a lunge line. A couple times a week, plus her walks and trots I would lunge her on a lunge line; no faster than an extended trot. (I wanted her to drive eventually; a driving horse shouldn't canter on a lunge line.)
My mare was looking pretty good by now. Her legs were straight and no longer flabby; her chest and neck were nice and firm. Her stomach was lean and fit as well. I decided to start jumping her in hand. She was very fit by now too.
About 6 months later, I began showing my mare. She brought home several ribbons in halter classes (even though she gets nervous at shows, and finds it hard to stand still longer than 3 minutes!), and even a few blues! It just goes to show that with these simple exercises you can turn a herd mare into a well conditioned show horse in months.
There are other various routines, like hooking your horse up to a golf cart and making them run with it, or driving them. My mare is currently training to drive and I have never tried the golf cart, so I am not sure what they do.
