Google Sandbox can be actually a sort of filter which affects newly created websites and they will not gain top ranks fast, even if they have high
PR scores and are powered by strong links. The mechanism has become active by the Google team to prevent new sites from reaching high spots online quickly, despite the actions carried out by their admins and owners. Addition of contents to the websites and building links for them in the course of time seem to be two useful strategies to mention in here.
The fact is that websites are to gain trust of Google and prove that they are valuable projects over the net and this will naturally take some time to be done and carried out. There are no shortcuts to name which can help bypassing the Sandbox filter, especially when it comes to having top ranks in very competitive niches which are targeted by thousands of domains and other websites. Information-rich websites seem to get out of ranking filters usually very fast in most cases.