The next time you see AdWords ads on a site that you'd like to target, look for the 'Advertise on this site' link in the ad unit. After clicking that link, you'll be taken to a page that provides additional information about the site and allows you to log in to your existing AdWords account. Upon logging in, you'll simply complete the three step site-targeted campaign creation wizard, and your ads will be eligible to run on that site. Easy, right?
So, remember to keep your eyes open when you're surfing the web, you might just find another great advertising opportunity.

