It's simple as all get out but often over thought. Two things to remember good cable has memory of how it was spooled, a natural curve. Work with that curve. A little goes a long ways, you can always load more but unloading not so much. It's kind of a feel thing to get it just right.
Actually I load some snares a little more or unload them a little if need be on the fly to get just the right amount for various sized loops for different animals or different situations. Unloading is basically the same as loading them, just curl them back slightly with your fingers if they are too loaded and form a stupid looking/functioning loop.