Google adsense-Unacceptable site content- reasons and tips to overcome

I have seen a lot of people asking for the same question. I submitted my site to google adsense, but I am getting the reply as

Hello XXXX,

Thank you for your interest in Google AdSense. Unfortunately, after
reviewing your application, we're unable to accept you into Google AdSense
at this time.

We did not approve your application for the reasons listed below.

Issues:

- Unacceptable site content

---------------------

Further detail:

Unacceptable site content: In order to participate in Google AdSense,
publishers' websites and application information must satisfy the
following guidelines:

*Your site must have been active for at least 6 months before you apply
for AdSense.
*You must provide accurate personal information with your application that
matches the information on your page.
*Your website must contain substantial, original content.
*Your site must comply with Google AdSense program policies:
https://www.google.com/adsense/support/bin/answer.py?answer=48182 which
include Google's webmaster quality guidelines:
http://www.google.com/support/webmasters/bin/answer.py?answer=35769#quality.


 If your site satisfies the above criteria in the future, please resubmit
your application and we'll review it as soon as possible.



---------------------

You can find more details and application tips at
https://www.google.com/adsense/support/bin/answer.py?answer=75109.

To update and resubmit your application, please visit
https://www.google.com/adsense?hl=en_US and log in using the email address
and password you submitted with your application. Our specialists will
review your account for compliance with our program policies, so please
make sure to resolve all of the issues listed above before resubmitting.

For a complete list of AdSense criteria, please visit:
https://www.google.com/adsense/policies?hl=en_US
https://www.google.com/adsense/localized-terms?hl=en_US

If you have any questions, you're welcome to contact us at
https://www.google.com/adsense/support/bin/request.py

? at any time.

Regards,

The Google AdSense Team

 
Well Google replies to each and every email submitted, but it might take some months for them reply. If your site follows all the TOS correctly then you would not get this email.
All you need to do is, read the TOS of adsense before submitting your site.
In short I could summarize the tips to get adsense approved.

• Make sure that you own a good domain(.com, .net or .org) instead of free domains.
• Add content to your site. Content should be adsense friendly i.e. Say No adult content or warez content or duplicate content.
• Don't know whether you have original content or duplicate content. Just go to copyscape and paste your url and check for it.
• Google always appreciates fresh and new content. In case if you have more plagiarism detected on your site. Its better not to submit your site.
• Add pages like About, Privacy Policy, Contact Us etc.
• Do add content regularly at least an article a week. Submit your site to web directories. 
• Build some traffic. Many might find this part as difficult, but one thing is for sure. If your content is unique, google appreciates your effort and promotes your site to the top. You dont need to do any special SEO to get top rankings.
• Once you get some traffic, apply for adsense. 
• Wait patiently and in the mean time, add more fresh content. Your adsense will be approved.

Best of luck.