Is your domain address starting with http://www. or http://…? If you are not sure and never heard of this can affect your ranking, then you should probably losing some value. Just use any backlink checker tool or Websitegrader and check how many backlinks you get for http://atniz.com and http://www.atniz.com (replace “atniz” with your domain). In most cases you will be able to see some backlinks in both type of domains. We can’t control the way people link to us. Some may give www or without www. The problem is google look at http:// and http://www. as two different URL.
So, if you have equally same number of backlinks pointing to both URL, you may lose half of the backlink benefits. I don’t have to explain how important a backlink to our site is. You can get all your backlink value using 301 redirect. Choose any type of your preferred domain and redirect the other URL. This will help to accumulate all backlink value to one URL which is supposed to be. You can notice some difference in SERP ranking within days or weeks. But, of course it all depends on the quality of your backlinks.
Link building needs a lot of work and time but quality contents gets your organic links. Those who benefited from you will recommend your URL in forums, blogs, websites, etc. Organic backlinks often comes from related contents and have high value in SEO. We can’t assume or have control over those who gives backlink to include www or without www. But, we can control our backlink value to point one URL.