Though I've been skiing for 25 of my 30 years, this past weekend I had my second ever lesson with a local PSIA Level 3. She wanted to work with me on my extension, specifically on my timing and direction.
We covered a lot, but the drill that stuck out most for me was the White Pass Lean. I'd never done this exercise before and at first found it difficult just to get the sequencing right and not fall over. It was very hard to commit to the pinky toe edge as my brain just couldn't will my movements in that direction. After one pitiful run attempting to do the drill, we went back up and did it a second time. These attempts were better, and for the first time really brought home the difference between extending towards the inside of the new turn vs extending "up like the trees grow." When I mentally focused on flexing the outside ankle part of my boot for the one ski that was on the snow I was able to link a few of the turns together. Between turns she had me do a little bit of a traverse to bleed off some speed in order to further isolate the extension/flexion movements from other forces.
Even though I was able to do the drill, I was (very) far from mastering it. I can't wait to get back on the hill and practice them some more.