Ad extensions are additional elements displayed together with a text ad – links to specific subpages, short bullet points, a phone number, business address, prices, or a current promotion. They have two effects at once. They increase the space the ad takes up, which pushes out competitors and raises the click-through rate, and at the same time they feed into the ad's score in the auction, so for the same bid they improve its position. Even so, most accounts have only the bare minimum filled in. Fill in every type that makes sense for your offer, and point the links to specific pages, not all of them to the homepage. Write the text so that it adds to the ad rather than repeating it. Track the performance of individual extensions and replace the weak ones.
See also: Ad Rank, Click-through rate optimisation, Ad testing.
