Good point on wicking.
I don't remember what video it was. But for the horizontal coils this is how I saw to go about it and it works.
Note: I cut my cotton sheets into ~6-8mm strips
1) take the backing off a strip of cotton, and pull about 1/2 of the fluffy inside off the strip (~2-3mm thick)
2) twist one end tight, just enough to let you feed it through your coil.
3) pull it through, there should be slight resistance, but not so much that you're ripping your cotton or tweaking your coil. (at this point I usually pull it back and forth a little bit.
4) pull it to the end leaving enough that it reaches the end of the juice well, then cut an equal length on the other side.
5) repeat if you have a dual coil (for me I use 1 strip for 2 coils)
6) This is the trick here, take the cap and push it down on top, start to twist it on then remove the cap. This leaves small indentations on the cotton right where the cotton reaches the top of the deck, this is your guide.
7) cut the excess cotton at and angle across that indentation, one side at the top(closest to the coil) of the indentation, the other slightly below the indentation.
8) Prime it up and tuck the ends of that angled cut into the juice wells.
9) top it off plug it in, fill your tank and you're off (good idea to close airflow when refilling, and also don't overfill).
For Vertical coil I did it a little different, and I know it's not optimal, but here's how:
1) build your coil, get it set up, then take the strip of cotton and pull the backing along with a little cotton (~1mm of fluff)
2) Start with that strip, you'll leave one end in one juice well and wrap it with the backing on the inside touching your coil. Leave the top longer lead outside the cotton. Wrap it around twice and leave the other end in the opposite juice well.
3) Pull your top lead down and secure it.
4) Done!
Very simple, not optimal, still working on modifying my deck to handle what I want to do with the vertical build (needed bigger lead holes, but it's proving a pain to drill out). I figure if I can get that going well I'll probably add chiminey holes for more juice and wrap more cotton around the outside of the coil to soak that up. All goes well it should be nice.