Ooo I have a Wacom as well c:
Well , I've started using the tablet not too long ago , sometime around the beginning of the year and I've tried different techniques that seemed right to me. So far, Gimp alone wasn't helping me too much , that is , until I ended up with ArtRage Lite.
What I do , Is I sketch on Art Rage .... Since it can sense how much pressure I'm applying to the pencil , my lines can be really light or really dark ( if I'm baring down on it ). Once I'm satisfied with my sketch ( Light to very slightly dark lines ), I copy and paste it into Gimp and I outline the line using the brush in Gimp.
I found that the more I zoomed in, the more control I had over the flow of the brush and the lines weren't too thick nor too shaky ....
You can try using this method if it'll help you , that was already mentioned or keep experimenting until you find a technique that's right for you.
Good luck ^^