I'm a long line skier. I started slalom skiing 4 years ago, bought a boat for the sole reason of learning to ski. We have a small club on our lake, consisting of only 3 of us now, but I still can get out relatively regularly.
I'm at -15 and have been successful through 34 MPH. Last season, I ran a few sets with @Sethski and learned some valuable pointers. I had hoped to get down to his place this fall, but no luck so I'll run a few with him this coming spring. Being that I'm a relative beginner, the biggest things I took from him are:
Body position on the ski - Ski Tall
Stack
Shifting of the body weight to allow the ski to "squirt" out.
I worked on those things all season and my skiing improved. I took a few -22 passes but none of them successful. I welcome the information coming in this thread and would like to tip my hat to @ozski for starting it.