Facebook ads are valuable tool in promoting your new release or a sale.
Designing your ad
Choose an image. It can be your book cover, or you can be more creative and design your image that consists of your cover, a short teaser and a brief description of what you are advertising (new release, sale, or another promotion).
Facebook ads are the most effective when paired with a giveaway, Amazon gift-card works well here.
As part of the giveaway, ask to share your ad, get added to your mailing list, add your book to their Goodreads TBR list. Don't ask for too much. Generally, asking for one or two things is plenty. And you cannot ask anyone to enter in a giveaway by purchasing your book. A condition for entering your giveaway has to be easily achievable and fair (should not require any purchase).
Here is an example of my recent Facebook ad.
How much to spend?
General consensus is that $50 is a good budget to reach enough audience. You can try out your ad with $10 to see what kind of participation you get and adjust your ad accordingly.
How to choose target audience?
Facebook allows you to specify your target audience, which really gets you thinking. Unless you spent considerable amount of time defining your target audience, this might be the first time you ask yourself: who are your readers? It helps to be as granular as possible. Although Facebook will calculate a much smaller target audience if you limit it, it is actually better to each a narrower but more relevant audience than everyone in the country). Since you are paying per view, limit your audience as much as you can.
If you are a romance writer, you can pick romance readers, age of your audience (which is a must if you want to filter out teenagers who might not be interested in your book, for example), their location (does your target audience live in big US cities?), their interests (do your readers also love reading Fifty Shades of Grey?) Be creative and really think deep about your potential readers. What do they like to do online and on Facebook?
What do you think about Facebook ads? What worked for you?