How do you eliminate duplicate content from being indexed by Google?
Setting your preferred domain: You can ask Google to just crawl and index one of them and you also remove all risk of duplicate content.
Setting a preferred domain helps your site retain the link juice even when a backlinking site links to a non-preferred version of your site.
after setting your preferred domain in Google Webmaster Tools, your next step should be to set up 301 redirects from all of the non-preferred domain links on your site to your preferred ones. This will help search engines and visitors learn about your preferred version.
Manually point to the canonical link for all the pages: Google recommends that you add a canonical tag to the preferred URL of your content. When a search engine bot goes to a page and sees the canonical tag, it gets the link to the original resource.
Set up 301 redirects: To reduce the impact of such duplicate content issues, set up 301 redirects. 301 redirects from the non-preferred URLs of a resource to their preferred URLs are a great way to alert the search engines about your preference.
By putting Noindex meta tag: The noindex meta tag tells the search engine bots to not index a particular resource. You can use the noindex meta tag to avoid having search engines index your pages with duplicate content.