Head to this link (and sign in if you have to), then make sure the “Ads on apps and websites off of the Facebook Companies” option is turned “no.”
And that’s it. The caveat is that you may see ads relating to your age, gender, or location, Facebook says.
You can also make other ad-based adjustments to the page — to Facebook’s credit, they’re fairly easy to understand. The best bet (at the time of publication) is to switch all options to “no” or “no-one.”