I've been reading up on novel writing, in preparation for leading a workshop for my critique group. We all seem to struggle with how to structure such and long, unwieldy beast.
One helpful hint that I've found is to launch the book with an "inciting incident," one that threatens the MC's basic sense of self. Then craft "set pieces," or scenes with high emotional impact, turning points along your character's path to the "inner cave," crisis point, and resolution. Jot these all scenes down on index cards that you can shuffle, remove, or add to until your plot line makes sense.