6 Google Ad Extensions to Supercharge Your Clickthrough Rate Ad extensions entice more clicks. Here are six different ad extensions you can try.

In their book Ultimate Guide to Google AdWords, online advertising and Google AdWords experts Perry Marshall, Mike Rhodes and Bryan Todd offer information that will help you get more clicks from Google for less money, convert more visitors to buyers, and make your online business more effective than ever. In this edited excerpt, the authors explain how adding extensions to your Google ads can increase your clickthrough rate.

Ad extensions boost clickthrough rates -- these extra links and lines of copy make your ads more visible and more relevant at the same time. And when you improve your visibility and relevance, you increase your clickthrough rate (CTR).

Here are six of the extensions available and how to make the best use of them:

Ad Extension No. 1: Sitelinks. If your ad is showing in one of the top three premium spots, you can show sitelink extensions. These appear as additional links underneath your main ad. They don't cost any extra, they offer more specific and relevant options for your prospect to click on, and they let you take visitors directly to the most relevant page.

Best of all, they take up more space on the Google results page, pushing your competitors and the organic search listings further down and out of the way.

Let's say your website sells a particular brand of men's shirts. You bid on the brand name as a keyword and write an ad that specifically offers a deal on long-sleeve crewnecks. With sitelinks, you can also add in three or four additional links in your ad that take visitors to offers for turtlenecks, short sleeve shirts or even hoodies, all from the same brand. Or you can highlight other information that may be of particular interest to the searcher, such as your "About Us" page, or your "Shipping and Returns Policy" page.

Ad Extension No. 2: Call Extensions. In late 2013, Google adjusted their editorial guidelines so you can no longer include a phone number in the headline or text of your ad. That's actually a good thing, because the phone number option is now available through the call extensions feature instead. Activate this, and the phone number of your choice will appear underneath your ad as an additional free line. That buys you extra space for ad copy and allows your ad to catch more eyeballs by taking up more space on the results page.

Call extensions are especially powerful when they show on mobile phones: You can set it so users click on your phone number and connect to you directly from your ad. That's particularly handy if you have a site that doesn't display well on mobile devices; better still, if the primary call-to-action on your landing page is to call your phone number. Your contact number will show at the top of your ad in place of your headline, highlighted in blue to indicate that it's clickable.

Ad Extension No. 3: Location. This is similar to call extensions except that, instead of showing your contact phone number, Google will show your physical location. This is an excellent feature for local brick-and-mortar businesses that want to increase foot traffic to their location.

Ad Extension No. 4: Images. If you want to increase the visibility of your ads, this is arguably the most effective of Google's ad extensions. Plus, very few AdWords advertisers make use of image ads. That's a huge advantage for you.

When you activate this extension, three images appear above your ads, featuring your product or brand. This is a great opportunity to simultaneously improve your visibility, your branding and your CTR. But it'll take some work to get this extension up and running. This only activates for ads in top position on the page, and you'll have to talk to your AdWords account representative to organize the setup process.

Ad Extension No. 5: Reviews. This specifically refers to reviews, not by individual buyers, but by reputable media outlets or blogs. This is another extension that's tricky to set up. To qualify for this, you'll need the URL of the webpage that contains your review, then either select a direct quote or write a paraphrased version of no more than 67 characters, including the source name. You then need to provide Google with the URL of the third-party site on which the review can be found. And you'll need to post the same quote on your landing page.

If you're willing to do the dance, once you activate it, this extension will display the review quote as an extra line below your ad.

Ad Extension No. 6: Annotations. Annotations are additional snippets of text or information that appear below your ad. They come in three types:

1. Seller ratings. If your product or service is featured on renowned independent review sites (such as Yelp, Bazaarvoice, PriceGrabber, Shopzilla, etc.), Google will compile the results and show your average rating out of five stars. You need to have had at least 30 unique reviews during the previous 12 months and an aver­age score of at least 3.5 out of 5. Be proactive with this, and ask your customers to leave reviews of your product.

2. Social. If your AdWords account is linked to your Google+ page, this annotation will display your number of followers or fans. This will increase your visibility by making your ad stand out. Plus, if you have a significant number of followers, it will add social proof, which can in turn increase your CTR and your conversions. To qualify for this extension, you must have a verified URL from your Google+ page, the domain of your Google+ page must match the domain in your ads, and your Google+ page must have what Google calls "high-quality posts and a signifi­cant number of followers." "Significant," in this instance, generally means 100 or more.

3. Previous visits. This feature is controlled entirely by Google. They'll displays your prospect's previous activity in connection with your website. For example, appear­ing as an extra line below your ad, it might say: "You visited xyz.com three times. Last visit: today."