Google Sitelinks

In most cases the websites which are at the top of Google pages and also powered by useful contents would gain the links. The No.1 sites in most niches are found to have some sitelinks and there is no way webmasters could manually add them to their websites because this is something only Google is capable of doing.

Its stated in Google Webmaster Tools. Sitelinks are decided by an algorithm which I guess no one knows.

On the google website it says that the structure of the website must be good to find good sitelinks.

authority sites has the benefits to obtain that advantage. on the other hand, you should also consider how relative and how valuable the content is. IMO

the structure of the website must be good to find good sitelinks.

Google will show the sitelinks, if the link will be useful to viewers. Otherwise i doesn't show it.

i guess some parameters are important for having Sitelinks in Google and they are Pagerank and traffic.

page rank and traffic are important ways to attain achievement

Like others said, it has to do with authority for your website and in conjunction with the phrase. For instance it is harder to get sitewide links to appear for your website on a generic search term, but much easier if someone searches an exact phrase of your website. It also pulls links from top nav bar and footer, and you can take away ones under webmaster tools and leave others if you want to cherry pick them.