Presence.
Do you look good? Do you exhibit confidence?
Technique.
Are your signals full and complete? I.e., don't just kind-of roll your wrists near your head for a TO signal. Get those arms extended overhead and cross your forearms. Come to a stop and signal incomplete pass, with arms fully extended to the side, parallel to the ground, and hold for several seconds.
Do you move with purpose and deliberacy, and stay focused on the action?
Do you know your keys? Hint: You can't know your keys without knowing everybody else's keys.
Do you maintain priorities? I.e., if you have a foul, are you able to continue to officiate until the appropriate time to make your report to the R? Keep your progress spot (if it is yours), until someone else can relieve you. Don't worry about the darned ball until opponents are separated and there is no real possibility of foul.
Hustle.
Hustle is not necessarily a sprint (although that is needed at times), but it is a solid, easy run, not a lazy jog. Sometimes a brisk walk can be good hustle, and better than a lazy jog.
Close in with hustle to the numbers, toward the dead ball - or farther as may be needed - after as many plays as possible. Check the action, then, when your presence is no longer needed, backpedal with hustle back to the sideline.
On COPs, hustle to your position on the other side of the ball.
Hustle will be noticed.
Be "coachable."
Don't try to show how much you know. Just let the events come to you. Some may think that asking a lot of questions shows interest and enthusiasm. Observers can see through that, and know it is just an effort to "suck up." But, a pertinent question or particularly astute observation at an opportune time can be a good thing.
Have a good attitude.
Be approachable to and by everyone. If there are bona fide ball persons, chain crew, etc., don't be afraid to introduce yourself and be friendly. They can be your friends, and we need as many as we can get.
There's more, but I'll yield the floor.
Robert