You’ve just written two pages of unique content for your website and two weeks later, you get a notification in Google Webmaster Tools that you are being penalized for duplicate content. What do you do?
You can claim your own content by using the rel=canonical attribute. This should be best practice because it prevents duplicate content penalties if someone should steal pages of your content for their own website.
To implement rel=canonical tags, simple add this code in between the <head> tags of all pages with unique content:
<link rel=”canonical” href=”http://www.blog.example.com/unique-content” />
Replace the example URL with your own.
The rel=canonical attribute is also useful for setting a preferred URL if you have multiple pages on your own site that have duplicate or very similar content. For example, this is used if you have a product page that has a dynamically changing URL based on the users options or preferences.