Once your book is sold, it is no longer about you. It is about everyone else.
This is another word of wisdom that comes to me through the experiences I've had with my wedding. As I learned early on, my wedding is about everyone but me. And like my wedding, your book, once it's been acquired by a publishing house is about everyone else but you. Before that point, it's just about yourself. You write whatever you want. It can be intensely personal. But after sale, it becomes about everyone else's needs. The editor has requirements. The publisher needs you to fit a market. Your readers want you to meet certain expections typical of your chosen genre. The moral of this tip is to enjoy that original time before your work sells. It's the last time your work is truly your own.