Since you’re an author, writing articles should be second nature for you. The more articles you get published the higher your stock as an author becomes. It goes without saying, your articles should relate to your book.
What you might want to do is plan out 20 articles by outlining what order you want to direct your reading audience. Remember to add a bit of intrigue to your articles to ensure that your audience will follow through and go to your website and buy your book.
Google search authors who have a book that is somewhat related to your book and ask them to post your articles on their website. Offer to post their articles on your site.
One of the things that I’ve gotten into the habit of is to carry a small notepad with me everywhere I go. When I have a few minutes I’ll make notes about thought that might make good additions to articles I want to write.