Ahh the easiest way is with paint, a brush and a steady hand...
As long as you can keep a decent point on the brush, keep the paint fluid so it flows from the brush well, painting thin lines should be as easy as doing it with a pencil. Practice painting thin lines on paper so you get the paint fluidity right and gain some better brush control.
Also worth remembering that it's easy to correct any mistakes in Black; having the confidence and know how to correct your mistakes is one of the keys to improving painting.