Training-wise, keep their attention on you with lots of shapes and transitions. Slow the gait down with your seat. Throwing in the occasionally rein-back can help rock your horse on his/her hocks, which makes it easier to collect for a slower gait like a jog or lope. Lots of half-halts!
In the show pen, western pleasure should be shown in a curb if the horse is over 3 years. Some smaller shows are fine with any age horse showing in a snaffle, however. If you're in a curb, you must show with one hand on the reins. The other hand can rest straight down to the side. For horsemanship (western eq) classes the free hand should be held up as if you were holding a spoon for egg-and-spoon. Give yourself plenty of room on the rail. Getting balled up on the rail with other riders doesn't help you, and can irritate the other riders. Give plenty of room while passing.