We're all different. I don't always start with the concept. Occasionally a publisher has said, "We'd like you to _________," and they let me know the theme or thrust of the book.
Most of the time, it's an idea that won't let go of me. I get ideas—lots of them—almost every day. Out of every 100, perhaps two of them have the kind of impact that sticks with me. I'm not one of those individuals who writes down ideas because that doesn't work for me. If the idea is important, I don't worry about forgetting it.
That's no guarantee a publishing house will offer a contract, but it helps me know what issues are hitting me. And occasionally, I've had a wonderful idea but the time wasn't right and five years later I sold it.
There is only one way to develop your book—
the method that works for you.