Storyboarding Multiple Narrators--How to Make Sense of the Whole Story

I get this question a lot:  When a book has more than one storyline, timeline, or main narrator, how do you make sure each storyline works individually? 

And, once you have each individual storyline in place, how do you weave them together to make sense of the whole?

Memoir and fiction has grown complex.   Maybe it's a reflection of our multi-tasking bra…