Be relaxed and humble in your ability. I see riders who think they are top material. Some, who think showing punishment to a horse is impressive. They ride with arrogance and forget that riding is a team effort, your teammate being your horse.
So I would look for natural ability. Your position should be correct and your signals clear. If I saw someone who was having a hard time doing something that should be relatively simple, I might second guess my decision. In no way should you interfere with a horse while they're working... ie: hanging on their mouth, unstable leg, bad balance etc.
I'm sure that's not you (: I am a working student at one stable and I just help exercise the horses, along with Ripley who is boarded there. I go out to ride him on a daily basis.
So I know that you might feel all eyes are on you (I know I did!)
But just stay calm, feel your horse and communicate. Be as helpful as you can without nagging. Use common sense. Logic. You'll be great.
distances are like men. never grab the first one you see; it's never the best one, more will come along.