Perhaps the easiest way to write a celebrity memoir is to have a relationship with a celebrity who happens to want to work with you as a writer. Of course, that doesn’t happen to most of us, so the other way is to develop your skills and publication history as a writer. It’s rare to find a celebrity who wants to work with a writer who has never published something. Even if you haven’t published a book, if your writing is well enough known in the magazine world, that may be enough to attract attention. But usually we want to see writing that has all of the elements you look for in a celebrity memoir: good storytelling ability, a strong narrative voice, and the ability to elicit stories from celebrities. Very often celebrities have things they want to talk about but don’t have a keen sense of storytelling. They might have all of the elements in their lives to make an engaging book, but it will take a writer to figure out how to craft those elements into a narrative and recognize which parts of the story need more attention.
So if you want to write a celebrity memoir, the first thing you need to do is become the kind of writer who gets noticed. You don’t even necessarily have to be primarily a memoir writer. I’m working with a writer right now who just finished a celebrity memoir, but before that, he had only published books on food. He was writing about soufflés and such, but we could tell from his writing that he understood storytelling and dialogue and character. Then he and the celebrity happened to click, and now she’s madly in love with his writing and wants to work with him forever.