At that age the first thing is just if you can play. I imagine your going to try to pitch so the first obvious thing is to throw strikes, next is your velocity and if you have any other pitches you can throw. If you can get people out at your age you should be fine.
Next would be attitude and if your willing to work hard. For example some schools are implimenting open gyms during the winter before tryouts, if your not playing a sport a good way to show the coaches is to make sure you show up on time at these events. Just work hard and have a positive atttitude.