You’ll want to have your custom audience (retargeting) pixel site-wide.

Then you can create any combination of audiences by url rule, days since they’ve visited, and so forth.

If you want to get pro, use Google Tag Manager (integrated with Google Analytics and free) to drive your Facebook, Google, and Twitter pixels. Then your pixels always run together.

Conversion pixels are a different matter– place those just on the confirmation pages.
The various networks are not clear about general retargeting pixels versus conversion pixels.
With the new Facebook custom audience pixel and a bit of technical wizardry, you can do without the conversion pixel, since you can fire multiple events on a single page.

Even if you don’t run ads, having the custom audience pixel site-wide gives you access to some cool analytics, helps you model lookalike audiences better, and also lets you create exclusion audiences for better segmentation. For example, you could set a rule to show ads/messages to people who are in your email list and have NOT been to the site in the last 7 days.

Url parameters (utm= in Google Analytics or CIDs in Omniture) lets you turn your Google paid search traffic and email traffic into custom audiences for automatic retargeting in Facebook, Google, and Twitter. Powerful stuff and easy to set up.

EzDrozGZUc8QajtOoeobKwRXOmq7w16mdz-LJj0ptjoIt is our job as marketers to find the best prospects for whatever it is we are selling. In the case of retargeting; this is some of the sweetest, lowest-hanging fruit you can find when looking for customers. It takes a number of touch-points to make a sale, and this not only puts you in front of users who have already had some contact with your brand, it also allows you to get back in front of people that might have been interrupted during their purchase decision, or possibly not ready to pull their wallets out just yet. -Franco Puetz

Many combinations possible when you start to cross your social, web, and email traffic.

All entrepreneurs and business owners should do this– just need a couple hours to get the “plumbing” in place and then a dollar a day for retargeting ad budgets.  Killer ROI.