I first start working on the image 4x the size I want in the end. In Photoshop, I use a 5 pixel diameter round brush with 0% hardness, spacing 25%. Amazingly enough, with a mouse, I use the Pen tool, making making each curve one at a time over the draft of whatever I'm tracing over (98% of the time, something I actually drew, this pic was just a colour test). Then I stroke the pen lines with the paintbrush tool. Some say I'm crazy, but it only took 30 mins to actually digitally ink this pic this way. Better quality is certainly worth the slightly extra time. When I'm complete with everything, I shrink the image to 25% percent of it's original size, giving nice, clean, yet thin lines.