I have used Facebook ads for years. First rule: Facebook *heavily* promotes ads that garner interest from an audience, automatically fine tuning your ad audience to find better micro-fits if your budget is small. If your ad does not generate user interaction, expect it to be expensive and slow.
To capitalize on this, Facebook works well for novel products for a very engaged target audience picked up front. Spend a lot of time to get people to interact, spend a lot of time developing the experience behind the interaction. These ads get high placement counts quickly, and typically get much lower ad costs. My understanding is that Facebook likes and reposts of ad content are free, so aiming to multiply ad ROI by this can be effective.
That being said, Facebook is now the 500 lb gorilla of targeted advertising. They are the only site that can turn regular demographic information into targeted ads without upfront expense. As a consequence, price per ad display has dramatically increased in the past few years, reducing ROI.
Pick the medium that bests suit your audience. If engagement and meeting significant customer information needs drive your business in a content-like fashion, Facebook still works pretty well. Otherwise, more traditional avenues may end up with better ROI, requiring less Internet-unique advertising practices to achieve results.