Put the cotton in the coil and give it a pull through. As you are pulling, it will start to have some resistance and drag as it goes through. Stop when it becomes hard to pull and may start moving the coil then back it out a bit, trim and you're good. If using a rta I'm not sure how much of a tail needs to be left on either side of the coil but try to see other folks builds to see. For my bottom fed attys I don't leave a lot of tail as I find it just hogs juice. Hope this helps!
