from a parent
Coaches will have more advice for you. I can give you a couple of observations from a parent's perspective, from when my daughter was in rec classes and had some teenage students for coaches.
They are only there an hour or two, please be "present" and watch each one during their turn when you are watching or spotting their vaults/jumps onto the mat. They have waited in line patiently for their turn to vault onto the mat. My daughter always looked right at the coach after she did something, and I could see her face fall when the coach wasn't watching or paying any attention to her or the class. My daughter wanted constructive feedback, a smile, high fives, or even just to know in some way that you were paying attention.
Smiles are free and should be abundant when working with small children.
Remember that they look up to you. I can't think of a gymnastics coach that my daughter hasn't liked, and she adores some of them. You are a big girl (an automatic plus in my daughters eyes), their gymnastics coach and teacher, and they think you rock. Respect that new position as a teenage coach and wear it well. You're the grown-up now (but a cooler one than their parents).
Even when my daughter was "only" in recreational classes at the the time, I appreciated coaches who kept the girls busy. The one and only time I switched my daughter out of a class was when my daughter had what can best be described as a lollygagger coach. I watched one hour, and my daughter literallly did only twelve minutes of exercise in that hour. All of it was weighting in line, sitting while the coach was fiddling with something, talking to someone, or waiting turns somewhere. I switched her into a different class time after that happened. Getting some exercise should be a given while they are there!
Good luck and have fun!