As an aging adult who still takes lessons one night a week (one night of guaranteed riding and no cat-herding of friends), I'll echo a few of the above comments:
1) less talk, more rock. If you can't explain a drill in less than a minute, then work on your explanation on the next lift up but move on to another drill. I want to do, not have doing described to me.
2) For me personally, be physical. Don't keep saying "get lower" over and over, I heard you the first time. Problem is: I think my stance is low. Next chance you get, put your hands on my shoulders, push me down and say "that's what I mean by low".
3) Don't be annoyingly positive. People can tell what is false praise. Yes, you want to keep their spirits up during a rough stretch, but clapping and high fiveing after every run whether they fell 20x or not at all annoys me.
4) Give me some tip or drill that I can use to self-assess when you're not around. For example, I know I have a tendency to not shift my balance fore and aft well when carving. It just creeps in turn after turn and I don't notice until I start washing out a lot more frequently late in the day. I used to think it was a starting sign of my old legs getting tired later in the day. My instructor gave me one stupid little drill that I can do to check up on myself and now I can tell that it's not me getting tired, it's me getting lazy. Best $20 lesson I ever had.