Help! My Facebook Ads Suck by Mal and Jill Cooper is one of those books I now believe every author should read. There isn't just information about ads in there (which is incredibly good and relatable), there's also information about marketing and different things to expect. It's helped me not only change how I run my ads but my release and promotional steps.
You can also get it for free on their website here: https://www.thewritingwives.com/free-facebook-ads-book