Sandbox is a very popular term for SERP rankings for new sites. Sandbox theory states that new sites are burried over by old sites on SERP page until the site aged.

I personally do not think Sandbox really exists. If a site is competiting for a very competitive or even medium competitive keyword, it makes sense that results from the new site yet have to establish the usefulness over the old ones. You can see the same in our daily lifes. We value people more who we know for long time. When we know somebody new, we take our time before really trust them all the way.

New sites although can get away getting higher ranking for low-competition keywords. I had seen that for several of my sites.

So what can you do to improve your rankings for your new site? I would suggest these:

1. Add fresh content often. This ensures that search engine bots visit your site frequently.
2. Submit your pages to sites that are very frequently visited by SE bots. Social networking sites fall in this category. Care should be taken to pick sites which fall in your site category.
3. Along with targeting higher competitive keywords, target long-tail keywords. This will get you some traffic to keep the hopes up. For bigger sites traffic from long tail keywords fills the major part of the daily traffic source.
4. Continually build backlinks. The key to building backlinks are getting links from RELATED sites and building links for different pages of the sites, not just the home page.