Here are methods you can take to know your audience better:
If you are sending an external communication to a company, determine its vision, its mission, its accomplishments and goals. If your letter reflects these things, the company would realize that you care both for its objectives and its situation.
If you are sending a proposal to an individual, know his/her preferences, pain, problem or wants.
You can also take a look at the company’s communication style through its public documents and press releases.