When you enter the ring its all about picking a good spot on the rail. If you're a novice rider, don't pick a spot right behind the spooky horse that bucks. If you know your horse's jog is faster than that super WP horse don't pick a spot on the rail near it. You don't want to be over taking it in 2 seconds. Setting yourself up for success start's from the beginning, so picking the right spot is essential.
Perfect reining back wards. This is something that can either bring you a place or lose you the class. I've seen so many people with wonderful horses only to be let down when asked to rein back. Make sure your horse knows the signals to move back and it isn't sluggish. He should have clearly defined steps and back straight.
I know a few more but I'm too tired to write more
And I'm sure all the other people on here will cover it for me.