You will need to have some traffic on your site to get them. Keep creating good content. Google will not give them easily.
Make sure your navigation is tagged with semantic HTML and include a login identifier
navigation on your menu. This will help Google know which links are your navigation. (as opposed to a list of links).
Plus, once you've found them, Google will give you the ability to control the links you want in your sitelinks via Google Webmaster Tools.
There is no simple way or algorithm known publicly to give you sitelinks. And I'm sure this algorithm changes all the time.
- Do not think too much about it and give it time, site links are rare.