I use a 5/64" drill bit to wrap my coil on a Kayfun style. Once you build a good coil it'll last a long time. I rewick mine every day or two, depending on how it's tasting. It'll taste off or burnt. Sometimes, depending upon the juice you're vaping the coil can get pretty gunked up, when rewicking I do a few dry burns (firing the coil with no wick, and the tank off) and clear away any gunk left.
To build the wick make sure your hands are clean. Tear off a piece of your cotton and work it together, do not twist it. Just tamp it in your fingers. Next, twist one end to a tip fine enough to slide through the coil. Pull the wick through the coil. It should be loose enough to pull through the coil, but tight enough to give a bit of resistance. Pull through enough to trim the twisted tip off, or untwist the twisted end. Next, trim your wick. Cut it even with the outside threads (the threads the tank screws onto). Now you will position the wick. Wet the wick with your juice. Not a lot, just enough to see that the wick is no longer dry. Then tuck the wick up on the deck, gluing it to the vertical side of the deck (directly beneath the coil). Tuck the remaining fibers up on the horizontal part of deck. Don't leave any fibers in the juice channel but place them over it. Repeat on the other side, put everything together, fill with juice using a syringe or needle tip bottle and vape away!