Ad extensions allow you to show additional information on your Google AdWords ads such as displaying map with business locations, linking to additional pages within the site, showing a click-to-call phone number, connecting your Google Plus account +1s, and showing product images, titles and prices (from Google Merchant Center). Google has reported that using ad extensions can increase CTR by 30% on average. Setting up Ad Extensions is fairly easy to do, simply check the “Ad extensions” tab in AdWords and look through the options there to set up. After implementing these options, keep an eye on performance to see what differences the extensions provide, and be aware you can check some of these performances by using Segment->Click Type in each AdWords page.
Read the full article here:
6 Ways Google Ad Extensions Can Improve Your AdWords Campaign – SEOmoz (blog)