There are a number of ways to market a book digitally. One way is to use social media platforms, such as Twitter and Facebook, to create a buzz about your book. You can also create a website or blog dedicated to your book, and use search engine optimization techniques to ensure that your site comes up when people search for keywords related to your book. Additionally, you can submit your book to online bookstores and directories, and use e-mail marketing to reach potential readers directly.