Creating new content, like articles and short pieces, based on your book or variations on your books theme is a great way to do just that.
Everything you write has the potential to generate book sales. This could be as simple as a book review on Goodreads, a blog on your website, or converting your book (or pieces of your book) into short fiction or article-length pieces to pitch to magazines or online periodicals.
You can create these pieces and offer them for free to newspapers and websites in your specific area of expertise or that cover topics highlighted in your book. For example, a novel about an exotic location could be perfect for an article or excerpt in a travel magazine or blog. Newspapers, online sites, bloggers, and magazines are always looking for strong content - and you are a published author! So put that street cred to work for you. In the bio included after your piece, you have an opportunity to mention your book and your website, which may lead to new relationships online (and down the road, new buyers for your book).
This type of content marketing is sneaky - it helps you build relationships and promote your brand as a contributor and author, all while giving you the opportunity to mention who you are as an author and send readers to your social platforms to follow you and learn more.
So write for free . . . and watch it pay off in sales (and great new relationships to boot)!
Here's a SmartBlogger article about writing for online publications, but there are others, just search on Google and start submitting!