What I have seen is that the most clicked on "and" consistent links on your website's homepage are the ones that are included here. So what ever your landing page is, the most clicked on links "from" the most searched "keywords" or relevant searches are what they use to display those Sitelinks in the search result.
So the links that bring in the most traffic to your site.
On my site there are 6 links that are clicked on daily more than any other, those are the ones displayed here:
Hope that helps out...