I discovered a blog written by Jason Fisher, Lingwë. He writes about a lot of writers I enjoy (J.R.R. Tolkien, C.S. Lewis, J.K. Rowling), and he recently posted about Rowling's writing scheme, complete with this image:
If you zoom in, you will see that these are some of Rowling's notes during her writing of Order of the Phoenix. It's absolutely amazing. Rowling has stated that she had the plot outlined in her head and knew what she was doing, but if you ever doubted, here is the proof. I love the columns for each subplot of the book. I've never attempted to write anything as complex as Harry Potter, or any work of fiction for that matter, but I can imagine notes like these would be invaluable in the process.