To help out, adwords want to help more, so giving sitelinks to the AdWords Opportunities tab.
You can also, get a personalized approximation of the impact on clicks and cost if sitelinks were applied, based on your last time campaign stats.
Offering you two guidelines, when you're setting up ad sitelinks:
Adwords systems automatically determine which sitelinks perform best and show them more frequently. So adding more than the minimum number of suggested sitelinks can boost your performance.
Sitelinks can come into view with any of the ads in your campaign. So choose website target and sitelink text that make sense across all of your ads.
To get more about the Opportunities tab, visit the AdWords Help Center.