firstly there aint anything like sandbox, the myth says, a new website stays in sandbox if it tries to acquire link too quickly. I think u meant supplemental , read matt cutts blog, i think he has explained it properly
Here is what you need... Secrets to Beating the Sandbox 2.0 REVEALED: The Ultimate Guide How to: Escape Google’s Supplemental Index Both articles by Mr Hagans Personally I have found the quickest way to get out of the supplemental index is by building links to a page with all your pages on, such as a site map or archives page. And I've found the quickest way to get out of the sandbox is to get listed in yahoo... and yes, it IS worth it!