When running Facebook ad campaigns, try and be aware of what stage your audience are in your funnel. If you are promoting a blog post at the top of your final, try and exclude anyone who might be in the middle or at the bottom of your funnel.
Use Facebook website audiences to exclude anyone who may have already visited a thank you or conversion page and use a tool like Sync2CRM to synchronise subscribers and customers from your CRM to your Facebook ads account.
Also make sure your subscribers and customers are tagged correctly in your CRM based on what they have downloaded or purchased. This is not a foolproof method as some customers and subscribers may have a different email address in Facebook, but it is the best option we have to make sure our re-marketing efforts are targeting the right people.