1) In the months and weeks preceding the tryout, attend any and all open practices, meetings and informational sessions. Make certain the coach knows you by name. If not, introduce yourself. Say "hello" each time thereafter, and indicate how excited you are to have an opportunity to tryout.
The remainder apply to tryout night:
2) Show up no later than 20 minutes early, fully dressed and ready to go. Look like a player, and treat this as the most important game of your life.
3) When the coach speaks, look him in the eye, and nod your head in affirmation. Resist the urge to talk with your friends or indulge in any horseplay. Your coach is looking for a player, not a class clown. If the coach asks you something, reply "yes, sir," with enthusiasm.
4) Sprint to and from each drill or station. Try to be the first in line.
5) Volunteer for everything. If the coach asks if you're interested in position "x" or skill "y," always reply "yes, sir!."
6) No matter the result, thank your coach afterward. He gave you an opportunity. Whether you took advantage or not is on you!