Once you know why you're writing, and what you're pursuing, then it's time to take a look outward. At your audience.
Know your audience.
If you're writing to be published, then this is essential. What do they expect? Your book will be placed on a shelf someday in a marked aisle/section. Who are the people perusing that aisle? What do they like?
This is similar to knowing your genre and the expectations inherent in it. Even knowing the necessary word count of your genre is important.
As writers seeking publication, we answer to more than just ourselves (as many of you said in last post's comments).
Are you "in the know" when it comes to your audience? Fill in the blank. A satisfied reader equals....?