I managed my first spin, a FS360 a few weeks ago. I did it line riding. I have managed a few 180s as well line riding. I want to get them down before attempting them freeriding as all of those have ended in failure so far.
For the start, I put the rope around to my back hand around my back and held onto the rope with my front hand. I then bent my knees, got low and not so much as spun, but carved up and through the wake. I kept that momentum going until I was facing the boat again. I was so excited that I pulled it off I bit it when I started fist pumping, lol. Try doing it with the rope first to get the hang of it. It can help you keep your confidence and balance until you get it down free riding.
I pulled the 180s without wrapping the rope, but got low and chopped the wake with my hand to help get the spin going. I didn't ride it switch very long and pretty much spun back to normal very quickly.
You definitely have to have your feet and your weight balanced pretty evenly to be able to spin and hold it.