One of the first things I do with clients preparing for a developmental edit is ask what they actually want from it—not what they think they're supposed to want, but what they genuinely need.

Are they feeling lost in the manuscript and need a collaborator to help them find their way? Are they hoping to level up their craft, not just fix this book? Are they mostly confident but want a second set of eyes on structure?

Those are different conversations with an editor. The more clearly you can articulate your goals up front, the more useful the whole process becomes.