Originally Posted by gmw
...You may write to the tone of the genre (romance, horror, etc.) or effect (fairy-tale, historical, etc), but to a particular audience?
That's a valid method of writing as well. Generally speaking, readers who favor a particular genre are also familiar with the tropes of that genre, and expect it in the writing... they become a genre audience. If you're not sure about the audience, therefore, you can target the genre and achieve roughly the same results.