Examine what's selling. Observe the themes and topics of books or materials that are in demand, and use one or some of them for your idea. Research the websites or blogs that attract the most visitors and jot down notes on what you think distinguishes these web pages. This can help you target an audience that is already open to what you'll write about.
Say you're drafting a work on Italian cooking, for instance. Heading to Amazon.com, you'll find that the most popular books emphasize simple, authentic cuisine that is easy to prepare. You could use this information, then, to create a cookbook featuring unique variations on Italian staples employing accessible directions.
Evaluate your gifts and specialties as an author. Reflect on what distinguishes your writing style and what you choose to write about. Then target an audience that would benefit from that expertise.
If you not only love dogs, but are particularly impassioned by Afghan hounds, consider working on projects that aim at fanciers of this breed. Should you be a poet, you could use the hound as a muse for an entire collection of your work. A writing especially skilled in nonfiction might interview a number of Afghan owners and research the history of the breed to write a book on the state of Afghan hounds today, as another example.
Write like a rock star. Create material targeted for a "fan" of your work. Fantasize that your audience cannot get enough of what you commit to paper. Or pretend that a prestigious publication has commissioned a piece from you for an upcoming edition or release. Such a mindset can lend specificity in detail and confidence in voice to your work, which in turn can attract and generate a self-selected audience.
Make a detailed list about your ideal reader. Meticulously envision her location, age, favorite foods, pastimes, and the DVDs and CDs she would want to enjoy on a desert island. Imagine why exactly she would be interested in what you write. Determine precisely what void in her life your writing could fill. This type of exercise can help you aim at a clear-cut audience to whom you tailor your work.
Evaluate comments and social networking, particularly for picking a blog's audience. Consider posting a small sample online of your work as it stands currently, encouraging people to respond with their opinions. You can extrapolate information about a prospective audience not only from the comments, but also from the demographic of the commentators.