Are you talking about Facebook ads? Retargeting is something you should definitely take advantage of along.
Check out Pollen (https://apps.shopify.com/poln) for help with your FB ads. Pollen takes your customer list and audience to automatically build lookalike audiences. The reviews are pretty high so you know there are customers who have successfully used it. Best of all, Pollen even offers complimentary ads so you don't have to design the ads yourself!
Hope this helps :)