Check out the how to guides; I wrote an article about spinning and it is straight out of the AASI manual.
A couple of quick pointers that may help, As you ride up the ramp, doing a quick edge change really helps with adding power to your spin. As you approach the jump, ride at it from a slight angle on your toe edge. Then, just before takeoff, briskly switch to your heel edge as you prewind. This really gets the spin going well.
To practice getting 3`s dialed in, I have found that "cheating" a little by picking a spot where I can ride up a bank and carve the first 90 degrees, pooping off my toes or heels and completing the 3. What this does is allows me to carve 90 dgrees and then I only need to spin 270. If you are doing 1`s, it is super easy to add just another 90 degrees of rotation. This allows the rider to focus on balance and landing without having to worry so much about achieving sufficient rotation to complete the spin. From there, it is easy to add the final 90 degrees off a small jump.
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