Sitelink extensions are the easiest and most common type of extension to include in your ads. Not only do these extensions help take up more real estate on the page to improve your CTR by 10-20%, they also have an impact on your ad rank. Previously, ad rank was calculated by using your max CPC bid and Quality Score. It now factors in ad extensions and formats.
For this reason alone, you want to make sure you have at least six active sitelinks set up for desktop, but also four active sitelinks for mobile. AdWords allows you to have up to twenty total per ad group or campaign. Even though Adwords allows you up to 25 characters for the link, I recommend trying to keep desktop sitelinks to 18-20 characters and mobile to 12-15 characters for the best CTR.
When creating mobile sitelinks take in to account the intentions of a mobile user and how it would differ from a desktop user.
Google will automatically show your highest-performing sitelinks on each format, so you do not have to worry about any type of placement on your end. Depending on the relevance of your sitelinks, you could even see lower CPCs and better performance. For the most value and optimized ads, be sure to add other extensions, such as seller ratings or call extensions.
Do not forget to monitor your extensions by looking at performance before and after implementation. You can segment your reports by click type to see a more detailed performance for different types of your extensions.
Since there are many factors and variables it is tough to pinpoint the specific extension change that had the most impact, but looking at an account overall within CTR and conversions, will allow you to understand that extensions are important for helping you and your clients.
Prepare for the August 2014 shopping search transition with Google Shopping and data feed optimization: