Welcome in this wonderful world! I think the others summarized it pretty well! So here are my suggestions:
- be confident, or at least look like you are
- don't be shy to ask questions
- Get them as active as possible
- get your hands at spotting... you might spot a cartwheel the wrong side as I did the first time (Good way to tell if the gymnast has stinky feet...). But the more you try, the better you become! You'll have the chance to coach littles ones, so it's easier.
- Talk to the parents. Everybody likes communication
- Be involved, praise, correct, encourage, do high fives, don't be shy to be ridiculous (by that I mean, dance with them, do the chicken as a warm-up with them...). You will soon have a bunch of drawings, school pictures and handmade cards as souvenirs... as well as parents telling you their kid just took the couch as a vaulting table the week-end before.
- Have fun and enjoy it... and in no time you'll see that the coaching monster has alienated your spirit and you just can't escape it. You'll think about drills, ideas, etc. while you're driving, dreaming, showering, eating, studying...