Even if you know exactly who your audience is, there are still up to 72 QUADRILLION possible varieties of combinations.

Our advice is to test everything. If you have more than 1,000 email addresses of people who are interested in your product, you can upload them to Facebook Audience Insights and find out the top interests groups, industries and other relevant data.  Healthy Facebook ad accounts end up having tens of thousands of ad groups with different targeting options.