In one of his blog posts, Matt Cutts said:
“Canonicalization is the process of picking the best url when there are several choices, and it usually refers to home pages.”
Lets say your home page can be accesses at -
http://www.example.com/
http://example.com/
People will find the same information at above two url’s. They won’t know the difference, right ? But search engines will. Googlebot sees the above two URLs as two different pages on the web.
Search engines can index both www and non www versions of your domain . Therefore, it’s best for SEO purposes to stick with one version of your domain and make sure all backlinks point to that version. The www version is recommended because most sites will link to you using that version anyway.
Once you have decided your preferred version ( www or non www ), you should implement 301 permanent redirects at the server end to ensure your preferred version is served no matter which version is typed in. You can also set your preferred domain within Google Webmaster Tools.
As far as ranking is concerned, there is no such preference from any search engine. The search engines will rank whichever URL has the highest number of quality links pointing to it.
Following are some tips for creating a Google-friendly site…
1. Give visitors the information they’re looking for
Provide high-quality content on your pages, especially your homepage. This is the single most important thing to do. If your pages contain useful information, their content will attract many visitors and entice webmasters to link to your site. In creating a helpful, information-rich site, write pages that clearly and accurately describe your topic.
2. Make sure that other sites link to yours
Links help Google crawlers find your site and can give your site greater visibility in our search results. Keep in mind that Google algorithms can distinguish natural links from unnatural links. Natural links to your site develop as part of the dynamic nature of the web when other sites find your content valuable and think it would be helpful for their visitors. Unnatural links to your site are placed there specifically to make your site look more popular to search engines.
3. Make your site easily accessible
Build your site with a logical link structure. Every page should be reachable from at least one static text link.
Use a text browser, such as Lynx, to examine your site. Most spiders see your site much as Lynx would.