What counts as duplicate content and how do you know if it's showing in the index?
Well, let's say that you have a blog. You have "Post A", which is totally unique content. However, that "Post A" is also showing up on a "category" page of your site. That category page is placed in Google's supplemental index and is considered to be duplicate content by Google.
How do you check for this?
Do a search like this in Google: site:http://www.yoursite.com
Now, go to the last page of results, if you see a message like this:
"In order to show you the most relevant results, we have omitted some entries very similar to the 42 already displayed.
If you like, you can repeat the search with the omitted results included."
- Click on "repeat the search with the omitted results included."
- Now, find the pages that are repeats (eg: the Category Page with Post "A"). Get the URLs of those pages and submit content removal requests to Google through Webmasters Tools: Completely remove an entire page - Webmaster Tools Help
- Now, the last step: put a disallow command in your robots.txt file so that URL is no longer crawled or indexed by Google.
URLs are usually removed from Google's index within 24 hours.
Use this strategy & witness a great improvement in your site's rankings! This strategy has helped me a great deal. Just thought I'd share it with you.