5 Direct Marketing Retargeting

http://www.retailonlineintegration.com/article/direct-marketing-retargeting-best-practices-boost-conversion/1

As any retailer knows, bad retargeting is nothing more than following abandoned consumers around the internet wasting money on irrelevant media buys. When done well, however, retargeting can provide great conversion rates at a lower cost per acquisition. 
The most profitable retargeting efforts focus on consumers who have either viewed products but haven't yet made a purchase or who did make a purchase and are likely to buy another related product. In either case, the overall strategy is to attract the consumer at the right time for the right cost.