The single biggest commitment you can make to marketing your book and writing is to create a newsletter. All advertising campaigns work better when augmented with a newsletter. This especially applies to AMS advertising. The reason is that the traffic and sales a newsletter generate can positively impact amazon advertising and category placement.
One of the quickest and cheapest ways to build a newsletter is to use Facebook marketing to target the kinds of fans that would not only like your writing but also potentially become superfans. The idea is to target those individuals on a long term basis. In other words, Facebook campaigns should be a permanent practice. The best way to do this is to offer what the industry terms as a lead magnet. A great example is offering Book 1 in a series for free to get people to opt into a newsletter and start a series. Then they get remarketed every book release. Once book two is launched the lead magnet can change into a novella or short story that augments the series. Note: Amazon does have a policy that prevents offering a book for free when it is published in Kindle. The industry term is ARC (advance reader copies) or the quest for beta readers. We find beta reader acquisition to be a low-cost marketing strategy.
We recommend starting with a $5 daily budget to grow the newsletter using Facebook ads. Typically opt-in rates run 20 centers to $1 per subscriber. Think of it this way for the cost of a daily Starbucks you can potentially own a newsletter fan club that sees almost 10k new subscribers per year. These fans buy new releases every time you publish a new book.