Authors of non-fiction books have considerable expertise in the subject area of their books – it's what made them qualified to write. When it comes time to launch a promotional campaign, book marketing companies increasingly recommend authors write bylined articles in relevant media. The purpose is to gain exposure and gently plug a book in the brief bio that runs at the end of the article. It's easy to see how it helps with publicity because once someone has read and enjoyed an article, they are likely to want to find out more, and buying a book is a natural way to do it. Media make room for good articles.
If you've never written a bylined article before, 700-900 words is generally an ideal length. The point is to promote your expertise and credibility (with media exposure provided by the articles) in the same topic area as your book – or a complimentary one. Always try to make the article about actionable suggestions, case studies, how-to- and other noteworthy ideas. It's customary for print and online media to publish an article with few changes and give its author a bio at the end. Few ways are better at attracting the interest of potential book buyers. People often want to find out more about a topic.
A bylined article often helps attract social media followers who are also crucial in developing an author platform (group of interested people). If you have a website, you'll want to give the web address, and you may also allow people to sign up for a newsletter if you write one. Media coverage is impressive to other media that might cover your book and makes an excellent impression with prospective readers. Because the most successful PR campaigns are incremental, bylined articles are one part of a multi-faceted campaign that reaches targeted readers. You want to convert them to book buyers ideally.
The most beneficial bylined articles written by book authors carefully consider the target audience. It's best if it is the same as the one for the book you've written. Book PR people are in the most vital position to submit bylined articles because they have longstanding relationships with the media. But authors can submit them directly if they've made media contacts who will be receptive. While it's common to want to publish an article in a media outlet with a vast audience, sometimes mass does not equal book sales. Niche media with highly interested audiences often produce far better results for authors.