flatspin 101 taught to me by Brian Bishop (yes, Josh BIshop's brother):
Step 1: on lip, dont lean into trick
Step 2:bring you shoulders diagonally back and thrust your hips opposite to your body.
Step 3: right after you gget the pop, look behind you and swing your far leg (i do a flatspin to the left, so I use my right leg as my far leg) in a horizontal semi-kick over across your body.
Step 4: grab japan to keep yourself in the acquired postion
Step 5: Don't float it too much because you will land sideways
Step 6: when you spot your landing, if you need to, let your grab go and swing your legs around to land
Caution: do not try this on a small jump. From experience, I can only do them off of about a 40, no smaller or I cant get the rotation since the "correct" way to perform a flatspin makes you soooo floaty.