Answer:
I use the ‘brush’ shaped brush and just play with the size, I don’t usually do lines with it so I don’t pay too much attention to the settings, I just slap the color on in there. I usually make my scanned lines darker by adjusting the levels and colors, if your lines look rough, maybe it’s the scanner resolution? I try to draw them smoothly and the scan is pretty much what the actual drawing looks like. I’ve found my drawings look rougher if I work on cartridge paper (standard sketchbook paper) so I try to work on either printing paper, which has a smoother surface, or moleskine sketchbook paper, which is 165gsm acid-free and very smooth.