Most visitors don’t buy, when they visit your webpage the first time. It is estimated, that consumer’s need about 7 interactions with your brand, before they are ready to buy. Thankfully, with Facebook & co it is much easier to create those interactions. It is called Retargeting (or sometimes Remarketing).
You simply address users that for example visited your website or maybe even added a product to the shopping cart but who did not finalise the purchase. You address them by creating a custom audience that includes everyone that meets your criteria (e.g. everyone that visited your website in the last 7 days).
The level of granularity in this matter lays in your hands. To get started, it is best to simply retargeting people who visited your website but did not finalise the desired conversion event (e.g. the purchase of a product).
If you want to be more specific, you can address people differently depending on how far they went in the purchase process. You can retargeting people that added a product to the cart but did not buy with specific ads highlighting that you are about to run our of stock, therefor creating a sense of urgency. (Note: you should always be truthful in your advertising. Communicating false information can seriously backlash at a later time!)
Duration: 5 days
Learning: Could work pretty well. Next time we would try a personal video invitation as creative, instead of a static image.