Many fiction writers write "for themselves," so they already know the answers to all these questions without even asking. The wonderful thing about having yourself as your target audience is you are likely to be passionate about the work, and that will bleed through. If you audience is similar to you or (as happens with some literary audiences) willing to meet you half way, you'll have a measure of success.
But writing for yourself in fiction can lead to stale writing for small or nonexistent audiences. Writing for audiences that are different from ourselves forces us to challenge our assumptions, come up with fresh phrasing and thoughts, and respond to questions. It creates a level of conflict that enlivens the work.
Of course, nonfiction writers (with, perhaps, the exception of memoirists) are lost if they don't keep the audience in mind. I write my technology blog for business people interested in innovation. I write my World Book articles for sixth graders who want some "gee whiz" and need to be able to explain what they read in class. I write speeches for impatient CEOs, distracted students, proud parents, skeptical scientists, and jaded Members of Congress. One size does not fit all.
I always explore my audience, whether I'm writing fiction or nonfiction. And my first drafts are aimed at one person -- usually an individual I know well. (Later drafts I adjusted to draw in others, but starting with the person who is critical to success gives the work focus.) Here's a bit more on the five questions I must answer:
- What are they interested in? In most case, you already have a topic that touches on the audience some way, but not always. Sales people, for instance, may have zero interest in how the widget they're selling works. They are likely, however, to want to look smart and knowledgeable in front of a client. Often, the writer has the subject right, but does not get the depth of information or the perspective right. Even if the answer seems obvious, this question deserves real thought.
- What problem or question do they have? When there is a major issue or problem at hand, the audience is not open to hearing about other things. When I worked for IBM, I always wanted to know if audience members had any negatives in their heads about the company. Internal speeches often dealt with pressing concerns before getting into the main topic. When you clear the issue, people are ready to listen.
- What do they want/need to hear? A common flaw in writing is the urge to tell the audience what the need to know. Business leaders want to shove their five key points into the heads of employees, and fiction writers want to deliver all the essential backstory in the first few pages (often in a prologue). In most cases, the audience needs to know less than the writer thinks. And even if they will end up needing the information, when and how it is presented makes a big difference in how it is received. A rule of thumb I use in fiction is don't give them anything they need until they want it (until they are begging for it). And it is amazing how that approach also works in nonfiction, especially if the material is intended to be persuasive. So focus on what they want, and make them want what they need.
- What's the right pacing? Some people like hard rock and some people like ballads. The energy and excitement of a work must match the needs of the audience and the intent of the work. Too slow is boring. Too fast is relentless. And what is the wrong pace for one audience may be just right for someone else.
- What voice will be most effective? An old trick for gaining confidence is to match the vocabulary, accent, and tone of the listener. Aligning the voice of the writing with that of the audience can be a great strategy. But it is not the only strategy. Often, we are looking for a voice of authority. If you are talking about my health, you'd better sound smart (and compassionate). If you are explaining blue grass music, it won't hurt if you sound like you come from the Appalachians. Finding the right voice for a work can go a long way toward engaging an audience. The one caution is that the voice must be authentic. Which means you need to really know and inhabit it, with all the care and skill of a dedicated actor.
The Web and googling organizations and people puts a lot at your fingertips, but don't rely on that alone. Talking to people, preferably face-to-face, can provide details you can't get otherwise. I don't advise stalking. I heard as author talk about how she followed teens in the mall and even took their pictures surreptitiously. Not a good idea, unless you also want to research the prison system.