I'm all for sharing useful tips.
With my work, I hand draw the illustration in pencil first then work over it in various thickness's of pens and markers. The work is then scanned and worked over in Photoshop, touching up smudges etc. After this I colour and embellish it with textures using the layer system. One major problem I had prior to successfully colouring my black & white images was erasing all the white so I could use the black line art as the top layer and place everything else underneath it to keep the line work crisp and bold.
I tried magic wanding areas and erasing them, I tried to do it all by hand, it would take hours to erase the white from one illustration. That was until I found this-
Hallelujah! Just load the action and play it on the scanned image layer to be left with a transparent layer containing just your lovely line art. After using this action I tend to defringe then reduce the brightness of the layer to be left with bold lines. Happy days! Try it -> PC White Out by PowerChild