Search engines seek fresh, unique content and give preference to websites that provide such. Duplicate content is frowned upon since the end user's results are meant to give them options, not the same content repeated.
So, what constitutes duplicate content? Well, the obvious one is posting the same exact text on several websites. Or, having someone steal your text and post it on their website. But what about the not-so-obvious?
If you are able to access your website with or without the www and neither one redirects to the other, then some search engines consider the two options duplicate content. Test your site out and see if one option automatically redirects to the other. If not, then a 301 Redirect is a good idea.
Example: realifewebdesigns.com redirects to www.realifewebdesigns.com
You can set this the other way around if you like. Either one works!
Using uppercase in page names and folders can cause unwanted duplicate content with search engines that distinguish between cases.
What happens if a user hyperlinks to your page with contactUs.html and another user hyperlinks with contactus.html? Some search engines will see these as two different pages with duplicate content. You are better off using contact-us.html or contact.html. The same scenario fits for the names of your folders.
Inbound links are a popularity contest and obtaining them from good quality websites is a great way to rank higher in the search engines. Include your keywords in the inbound links whenever possible and vary the hyperlink text to avoid being tagged as an inbound link spammer.
Submitting your articles and press releases online is another way to increase your inbound links. Remember to include your url (http://www.????.???), and equally important, create several variations of your articles and press releases by restructuring the consent so you are not submitting duplicate content to many online services.
Duplicate content, on your site or with another site, can lower your website rankings. The duplicate content filters used vary by search engine, are kept secret, and are fine-tuned as spammers find new ways to trick them. Look for ways to minimize duplication and provide fresh, unique content on a regular basis.