What metrics should I track for Facebook ads?

The most important things to look for are Ad Impressions which track ad clicks, Relevance Scores which track the relevance of ads within the content it appears on, the geographical location of the person seeing the ad, Various Audience demographics, Cost per result statistics that determine whether or not its worth the money, as well as video views, total clicks ad video watch time. There are a few more, that the ad system itself will tell you about.