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Showmanship, it's become one of my favorite classes, and it's pretty challenging too. IMO, it's great for two reasons: gives my horse a break and a challenge, as opposed to drilling for WP every day, and it has done wonders for his (usually good, haha) ground manners.
Basic Stuff:
Walking---> Um, duh. Self explainitory, but you do have to remember to always line your horse up with the judge when walking. I forgot once, and the judge mentioned it. Oooops!
Walk-Trot and Trot-Walk transitions---> Basically, they need to be pretty flawless. It will really help your "togetherness". Lots and lots of at-home practice, but you do halter, so I'm sure you've got this covered! Some patterns will call for a halt to trot transition, as well.
Setting up---> Should be accomplished in 2-3 seconds/steps. The more exact, the better. You then follow the "quarter system" to present your horse to the judge for "inspection"
Trotting---> Practice in straight lines, and in circles. Many patterns call for trotting circles, and it can actually be fairly difficult. As the handler, you need to be visualizing exactly when to turn, because your horse can only follow your shoulder/general body cues.
The pivot---> On the right hind foot. This was personally a huge source of frustration for us. What I did was once he got even two steps of a pivot, I'd say "Good Boy" and walk out of it. Eventually, he built up the endurance to do 360's, 180's and 90's, which are the most common. However, some patterns call for a 450 or worse!
The back---> Usually it'll call for 4-5 steps, in a straight line. Again, straightness is really important, and it should look like your horse enjoys it. Ha! Well, maybe not enjoys, but it shouldn't be a struggle. Some more complicated patterns will ask you to back in a semi-circle around a cone. Craziness!
In general, your horse needs to be spotlessly groomed, and your appearance should be very neat. As in, hair in a bun, pah-leazzze. No flopping ponytails, ick! Your horse should be very responsive to you, stop squarly and exactly. Smile, say "yes ma'am, no sir," and you'll do awesome!
I know I've forgotten about a million things, and someone please correct me if I'm wrong. I can give you what a typical SMS practice for me is, if that would help too.
Enjoy!