Like Eubanks said, slowing the boat down and lowering your center of gravity will help lots. Personally, I find surface 360s to be easier to spin backside. The handle pass is the hard part, but if you start from the cuffed position, you can actually spin the whole 360 without having to worry much about passing it.
Start from the cuffed position(looking backwards, two hand on the handle, handle behind your back, as if you were making a handle pass). From there, once you start spining the first 180, the rest will be easy.