I know, it's already a few pages back, but I'd like to say something about the "shading" topic: Please, for heaven's sake, don't use the "Burn" tool. ^^; Same for the "Dodge" tool. They don't look good when it comes to overall shading.
The most simple method is to copy the layer where your colouring is on, then Lock Alpha. Take the Eraser tool and erase the colour on the copied colour layer. Set it to multiply and the colour seems to disappear. Then take another colour (grey usually makes the colours look dull, try to experiment with green, blue, purple or red

) and begin to shade. You might have to try a few different colours until it looks good, but it's definitely better than the burn tool. The thing with the copying and the Lock Alpha helps you to stay in the lines. Even though you can't see it, the Oekaki still knows where the erased colour has been and won't let you colour anything else.
