Books on marketing for writers:
Social Media for Writers is a book that goes through the various social media platforms (Facebook, Twitter, Instagram, Snapchat, etc.) and how best to utilise them as a writer.
Services for Distribution/Marketing
Bookfunnel (starting at $20 per year) is a distribution/promotions website that allows you to cultivate an e-mail list, run promotions with other authors of your genre, and create giveaways where your readers can get a non-shareable link to download your book. They provide such things as Reader Magnets, ARC giveaways, Direct Sales, In Person Sales, and Extras.
Kobo is a book distribution service that partners with WalMart as an alternative to Amazon’s KDP that allows you to promote and distribute your ebooks and audiobooks. It has over 5 million titles already and is constantly growing. It is also a self-publishing platform (more on the publishing resources page) that allows you to promote on the kobo website, with expanded distribution to other places. Signing up for the distribution service is free.
Facebook Ads is a fairly common way for writers to reach an audience. Here are a couple of guides to using Facebook Ads: https://selfpublishingadvice.org/book-marketing-how-to-optimise-facebook-adverts-a-case-study/
Bookbub is a fairly popular way for authors to promote their books. Bookbub allows authors to run promotions through them and there are many people who subscribe to the mailing lists for book promotions. Bookbub also lets authors drive preorders, launch a book, and promote discounts. It has a very large reach. Signing up is free and many of the marketing tools are free, but there are some fees for running promotions.