Kevin Lee provides help with cutting "through the hype" to figure out what retargeting program to use. "Most importantly, you need to know when two retargeting programs are incompatible with each other (meaning you may have to pick one vendor with whom to work)," he writes.
He provides a primer on the three kinds of retargeting programs: search visitor recapture, targeting-driven, and publisher-driven. He also suggests starting with a strategy that lets you target search visitors to your site first. Existing customers and those who visit your site have a stronger tie-in to your brand than others.