There are many different reasons why your website may not be currently ranked within Google search results. Google have a very sophisticated algorithm that is comprised of over 500 different elements/ variables, so there is huge scope to identify what is right or wrong with your website. This is the job of a high-quality inbound marketing or search engine optimiser, as they have the experience to test a number of hypotheses into why your website is not ranking well.
Some generic reasons why your site might not be ranking is a lack of search engine optimisation, you have no content, your website is 100% flash-orientated, lack of marketing ability, no external links to your website, or your website might not even be indexed yet.