Here's a pencil drawing from one of my favorite cartoon bloggers Pedro Vargas. The first step is to open it in Illustrator and save it as an AI file. Next select the drawing and change the transparency to around 50% or whatever you're comfortable with. Lock this layer and create a new one above it.
Select the brush tool and make sure you're on the top layer. Initially I like to go for what I think should be the heaviest lines. For me the larger forms or shapes should have the thicker lines.
Next I go for the medium weighted portions. Try to use the line weight to describe a characters form and mass. For the most part I avoid parallel line weight for the same reason you should avoid parallel lines when drawing an organic shaped character.
I use my smallest brush for all the details. Don't get lazy with the small lines. They still need varying line weights to stay interesting.
Turn off or delete the pencil sketch layer and you're done! Next week... coloring!
Hold the option (or ALT key for you Windows types) while in the brush tool and quickly draw over a selected line to smooth it out. Very helpful, but don't overdo it... you don't want to kill the 'hand done' aspect!
Switch to the white arrow tool to reposition points on a selected line.
Hold down the option/ALT key with the pen tool to remove unwanted to excessive points on a selected line.
Don't forget you can adjust your Wacom Tablet preferences for additional control over the feel and functions.