This Mashable article provides 6 great tips for how to effectively test different versions of a Facebook ad.  Our favorites:  #1) Only change one variable at a time – this means creating different versions of your ad that only changes one of these elements at a time: the title, the picture, the main ad text, or who your ad is targeting.  #4) Always create a new ad – Facebook makes it easy to create a new ad based on an existing/past ad (click “Create Similar Ad”).  This pulls up your ad editing panel with all the information from that ad and allows you to edit each of its elements.  Check out the article for additional tips.