People often ask me why they can't get approved for AdSense. It's tough to answer because I do not work for Google, so I can only guess.
Many times it's because there are not enough pages on your website. I tell people to shoot for at least 20-30 pages at the very minimum, and make sure your content is very niche -- centered around ONE topic.
Google doesn't like sites that cover too many different topics because it's hard to target ads. The more focused your content is, the better.
In addition to more content, aim for longer articles (at least 700 words or more). Google does not like "thin" content sites that look as if they were created just for AdSense. Put some meat on those bones and make it look as if you put some effort into your website!
Also, check your grammar, spelling, layout etc. Remember you are partnering with Google and they don't like to see messy sites with poor/confusing navigation structures.