Whether you're writing or marketing fiction or nonfiction, you must understand your audience before you begin. Knowing who you are talking to helps you decide what to say and how to say it as well as where and when to say it to them.
People are accustomed to different vocabularies, value systems and levels of understanding.
You will be able to speak more clearly to your audience if you can sketch an accurate picture of the people in it. Take some time to create a profile of your typical reader. Once you've answered those questions you can learn more about your audience with help from local resources. You can also use the checklist to assess your awareness. You can narrow this down to a range, say 20-40, but don't leave it too broad, since it can tell you a lot about your reader.