Actually I don’t use vector lines, I use raster! I draw on large, high-res canvases and give my lines plenty of attention to make sure they have the smooth quality I want. If needed, my files are often big enough to take into Illustrator and convert to vector graphics without much fuss. I’ve taught myself how to use illustrator, but generally find it cumbersome and inorganic, so I prefer to use drawing programs like SAI or manga studio for my art.
I don’t have any tutorials or anything, my drawing process is pretty straight forward (sketch > ink > color), I’m just very meticulous when it comes to line work!