Shit man, you don't have to pay me, I'll tell you for free.
There isn't really a whole lot to it though. I use the basic sketch + refine with clean lines process. I think the trick is that people see a clean lineart piece, they think that it was all done in one go, when really what you're doing it laying down initial line groundwork, and then zooming in and going over almost every line, thinning some lines, thickening some lines, filling in some parts, so that when you zoom out again you have a great illusion of movement and depth.
There isn't really any special technique, it's just time and patience. If it helps at all I tend to do my lines with an airbrush set to 90% opacity, and instead of solid black I use dark grey or dark brown. I also set the lines layer to multiply.
Next time I'm doing lineart I can record the whole process and post it to my Twitter if you'd like. It's pretty tedious though!