When I was in graduate school at Marquette University, I had the opportunity to see their amazing Tolkien collection. Among the displays of Tolkien’s handwritten LOR drafts, I saw an interesting chart Tolkien had made for himself. At a point where Frodo and Sam are in Mordor, Aragorn and company are fighting somewhere else, and Merry and Pippin are with the Ents, Tolkien had drawn parallel vertical columns on a page with one column dedicated to summarizing each line of action. Items that lined up with each other across the columns were happening at the same time–he had written dates in the margins to get the chronology exact. This arrangement let him see, for example, what Pippin was doing in the forest when Aragorn was fighting a battle at the city.
I have never seen this technique described in a book about writing, but it sure makes sense to me. So when I reached a point in my own story where I couldn’t keep the interweaving plot lines straight in my mind, I had a white-board session with a vertical column for each major character:
I don’t know how the story ends yet, but I’m really hoping it ends faster than the Lord of the Rings.