There are several ways to learn to do a flat 360. My favorite is this one:
Learning the fundamental building blocks of a flat spin
1. Ski forward down the hill. Slide/pull back one foot but not the hip above it. Let's say pull the left foot back. This should start a left turn or a left rotation all by itself. Pulling that foot back involves bending the left leg a little. It puts pressure on that ski's tip. The pressure will produce drag and cause you to turn or rotate to the left, with most of your weight on the other ski. You may get a turn to the left with leftward travel, or you may get a rotation to the left without that travel.
2. Mess with the effect the pulling-back causes to strengthen the rotation and diminish the travel. See how far you can get that rotation to take you. With work, you should be able to get yourself pointing uphill.
3. Slide backwards and point your skis downhill again.
4. Repeat this sequence in both directions over and over until you can point your skis uphill in both directions, then return to pointing them downhill. All the while you will be moving downhill. Your goal is to eliminate left-right travel.
5. Bending your ankles (closing them) to move your body more forward aka down the hill (think: ski jumper) for the first half of each of these helps. This puts your weight over the fronts of your skis, so they will pivot over their shovels.
6. Conversely, open your ankles to move your body weight downhill over the backs of your skis for the second half when you are rotating to point skis downhill again. Leaning backwards over your skis feels odd; work to get familiar with this. The skis will pivot back around on the tails.
7. When you get this going, you will be pivoting on the front of the right ski to rotate left to point uphill. Your weight will mostly be on that one ski. And when you pivot to point downhill, you'll be pivoting over the tail of the right ski.
Putting those building blocks together to get the spin to work
8. You now know how to do both parts of a full 360 in either direction, although you haven't done one yet. The first part of the left pivot (pull left foot back while closing the ankle to move weight forward, causing a pivot over front of right ski to point uphill) needs to be combined with the second part of the right pivot (lean back, pivot skis around to point downhill, standing on left ski).
9. Summary: for left spin, stand on right ski for first part, stand on left ski for second part. Also: stand on front of right ski for first part, stand on back of left ski for second part.
10. I say to myself out loud on a left spin (to keep me from getting mixed up on which ski to stand on): right ski, left ski. That helps enormously.
11. So when you are pointing uphill, switch which ski you are standing on, lean back, and around you'll go using the angular momentum you've built up. You need to be spinning without travel for this to work well. Pause, and you stall.
12. Getting the skis to point back downhill is the hard part where mostly everyone stalls out. It takes adults a while to figure this out. Kids just get it. So annoying.
