First, get a regulator spool. Don’t mess around with line coils without one. It always ends up a rats nest. The $30 regulator is worth it.
Regulator Spool | Scientific Anglers
The Scientific Anglers Regulator Spool streamlines swapping fly lines on and off your reel, offering fast, tangle-free line management in any environment. The perfect tool for organized, hassle-free gear changes on the water or at home.
How to use it:
To figure out how much backing you need, Tim Flagler recommends putting on your line first, then the backing, then stripping it all off and putting the backing on normally. It takes longer, but you get the right amount every time without guessing.
Use a loop-to-loop connection: