In showmanship, horsemanship, and pleasure classes, regardless of discipline, ALWAYS know where the judge is and where other horses are.
Make sure your horse is properly conditioned and relaxed.
Know the pattern inside and out before you step on your horse or pick up the lead. I like to do a mental walkthrough several times before I go in the pen. Pay attention to little things, like which side of the cones you're supposed to be on, that you don't run over a cone (done that before!), how many steps you're supposed to back, which direction you're supposed to pivot or sidepass, and if it calls for circles, that you make an actual circle, not an egg or some other shape. Oooohhh, another important one is which lead you're supposed to take.