Mostly it's just the way they teach you in "The Simpson's Handbook". Even with the guides though the hair never looks right - I've never seen anyone get it to look the same way it does in the show. With the possible exception of *Simpspin, but he's just incredible.
That's all well and good until you want to draw an original pose. Then it's almost impossible to get the hair to line up with the body properly. Nah it's better to draw it from scratch or at least copy freehand rather than trace. People will let you get away with a lot when it comes to her hair cause we all know how difficult it is.
I drew it in sketchbook pro with my tablet and saved each stage as a jpeg, then added each jpeg as a new layer in photoshop and turned them on or off for each frame (there are 52 frames) and saved it as a gif.