Toph:
The key to Earthbending is your stance. You've got to be steady and strong. Rock is a stubborn element. If you're going to move it, you've got to be like a rock yourself.
This quote occurs at 00:02:36-00:02:48 in the video.
Aang begins to learn earthbending from Toph; Uncle Iroh resumes teaching Zuko firebending to better prepare him for facing Azula, and reveals a new technique he learned from watching waterbenders.