Okay, you said you wouldn't mind tips. If you first cover the entire drawing with a solid color, that will avoid those white bits. And using layers really prevents accidental erasing of the lines.

Now you have pretty much white what would logically be dark.

Would you like tips?

It's not required to write your name here to keep people from stealing stuff. Just e-mail it to yourself. I'm sure I did it once or twice here.