(This is for lineart)
http://pheona.deviantart.com/art/Lineart-tutorial-for-GIMP-27643748

(Coloring)
http://nanidanides.deviantart.com/art/Simple-GIMP-coloring-47397015

And pretty much any one on this page as well.

http://browse.deviantart.com/?qh=&section=&q=coloring+tutorial#order=9&q=gimp+coloring+tutorial