Focus on consistency, staying in the proper frame, and work on those transitions. They should be rock solid and non-eventful. And don't rush. I know it drives non Western Pleasure folks crazy, but don't be the first (or second or third) to respond to the announcer's instructions. If they say, "lope your horses," don't just push into the lope immediately. Take a second to ensure you have a good place on the rail with the previous horse aways ahead of you (especially if you're not super slow) and then get your horse in frame before you start loping. Keep calm, go slow and be intentional and smooth. Stay on the rail and don't go racing around the center. If you're passing horses, there is something wrong. Go home and work on it again before the next show. And have a friend video you at the show, and be sure they catch a little video of the winning horses too, so you can see the difference.
A good trainer will help you do all of this too. :)
Good luck and have fun!!