To get good rankings in Google it is necessary to have incoming links from relevant sources. Having links with keyphrases related to your site is a start. It is better to have links from sites that specialize in your topic, rather than generic directories or unrelated sites. Getting a link to your site on a page with high PageRank is best. PageRank is a general link popularity measure by Google – typically pages with higher PageRank are considered to be more important, more trustworthy. A site with high PageRank will have more of its pages indexed. To get an idea of where your PageRank is at, you can download Google’s toolbar. The number displayed on the toolbar isn’t what Google actually uses, but it is still useful for getting an idea of a page’s link popularity.

Aging Delay or the Google Sandbox

New sites are repressed by Google for around nine months from when the site first got links and appeared in Google’s index. This is Google’s aging delay. Getting links from very, very highly reputable sites can help your site bypass the age delay. Google doesn’t talk about a sandbox effect, but they’ve filed a patent application that discusses using link history to rank sites. It may be an effect that arises because a new site hasn’t established a history of links. If you have a new site, all you can do is wait. Your site won’t show up for terms other than those similar to your company name for at least nine months.

Other Factors

Google is always looking for spammers. Sites are supposed to acquire links based on the merit of their content. Buying links might not help with rankings, and becoming a part of an artificial link network could result in penalties to your site.
Other factors that Google probably considers in its algorithm are who linking domains are registered to, how long it will be before your domain will expire (serious sites will commit to longer domain ownership), and who your site links to.