I've just written a simple tutorial on the method I use GIMP to prepare my comic using nothing but GIMP to draw the panels. Not super detailed, but will give you some clue as to how I use layering and positioning to make things simpler and easier and also re-use backgrounds.
Take a look: http://harishankar.org/blog/entry.php/h ... ly-in-gimp
Judicious use of layers and layer effects can be tedious but will have dramatic improvements in the depth and richness of your comic strip. Also using layers wisely allows you to focus on one part of your comic (say a character) alone without worrying about messing up other parts of your drawing. I also found that backgrounds are much easier to draw without the superimposed characters first - just make sure your characters don't "float" in the background though. This can be a problem when doing things in this technique...
