I think you're site is new based on your statistics:
Threads 1,758
Posts 26,979
Members 1,615
Active Members 357
But as your site grows more popular, Google will have sitelinks to the most popular shared sections within your site. Also a good way is to add direct links within your header to the most popular pages that is relevant to your site. This tells Google that these are important sections/pages within your site.
Take a look at this site for ex
https://www.google.com/#newwindow=1&q=animenewsnetwork
If you visits
http://www.animenewsnetwork.com , you will find that these site links within Google are sections on the site's header. It has to be relevant and popular though to your site.