It's difficult to predict how a specific ad will do as it is based on a number of factors (the time of week, time of year, what's in the news, relevance to your audience, imagery, the campaign page itself, how much you invest, etc.). However, for a typical campaign, we will generally see an average of a 4x-6x return on investment.
For each campaign that we run ads for, we will typically test out a few different target audiences in the first few days to see which has the most positive results and then stick with the audiences that do best for the rest of the campaign.