What are some valuable things you have learned in agility from your instructors?
It's not agility, but it applies.
Before I was ever allowed to start training my first dog in obedience, the importance of footwork was beaten into me. I spent a month learning how to cue the dog with my legs, how to do perfect turns, and a perfect halt.
I spent 12 years doing ballet, so it didn't take me long to figure out. And four CD's later, I can train and put a CD on a dog fairly quickly.
Anyway, that translated somewhat into agility. Consistent body cues, and overall obedience training makes for a better agility dog. I think once, maybe, have my dogs broken a stay on the start line. Generally, they do obedience first, then agility, so they know STAY before they ever hit the agility ring.
I can tell the obedience handlers from the agility handlers who have never done obedience, just from the set up and first obstacle.