I watched my son having a lesson a few years ago and immediately clicked with the instructor and went back to her for lessons myself. I got frustrated with my riding during one exercise she'd set and ended up crying. Her advice, "it shows you care, keep going, you'll succeed".
In a Ride With Your Mind lesson years ago the instructor told me to throw my vision forward, around the circle I was riding, it stopped me fixating on bend and flexion. It is easy to ride forward outside hacking but one becomes a bit obsessive indoors schooling!
Another one I remembered - your reins act like holding a young child's hand as you cross a road. If you let go they'll be confused and scared, if not they'll trust and follow you. Obviously your horse won't panic if you drop your reins but they need your hands and leg there to move forward and put their trust in you
A few things have really stuck with me:
R.I.B.S when jumping. Rhythm, impulsive, balance and stride in that order. The reality is that if you get the first 2 right, the second 2 usually follow.
Riding with the leg to hand is like squeezing toothpaste forward out of a tube.
Riding a 20m circle by going around the numbers on a clock face. I can still remember my PC instructor getting me to change the rein though the circle by calling out the numbers!