Excellent advice: Knowing "why" you're writing a biography is the first thing you need to begin with!
I’ve written three biographies, each with a different purpose and for specific audiences—but the why behind each story is what helped to make them work.
My grandmother’s story was written to preserve her life in chronological order as part of some family history we were working on.
An entrepreneur’s story was an account of overcoming adversity. It was meant to inspire her worldwide audience and illustrate the power of personal stories.
A YouTuber’s story was an account of success at the near-loss of his integrity and his reasons for becoming a public figure.
I've actually just written about this on Medium too. I think it's so important to tell life stories ...