The first and the most major factor that will affect your website’s search engine ranking and page rank will be its domain. For example, this blog is having two domains ,i.e., http://webtalks.blogspot.com and http://www.webtalks.blogspot.com.
Any person will say these two means the same thing. But you are wrong. Googlebot and other search engine robots take this as two different websites. Now all my backlinks and page rank is on the http://webtalks.blogspot.com domain. What if a person visits the other domain and says this blog is not even indexed by Google! Now I kept on thinking what can be done to solve this major problem.
Then I ended up with two main factors.If you are submitting your site to a directory or any other website, make sure you submit the same domain only. If the directory has the different domain, change it immediately .
To prefer your domain go to Google Sitemaps, verify your site and then choose preferred domain. If you have any problems with verification of your site, you can have a look at A Complete Blogger Guide.