When you are setting up your WordPress blog, you will be given the option of setting your URL with a WWW or without.
To do this, in the left column of your WordPress dashboard go to:
Settings > General
In this section you will see:
WordPress address (URL)
Site address (URL)
In these boxes type in the full URL you wish to use. For example I have set this site as:
http://www.travelbloggersguide.com over http://travelbloggersguide.com.
Which ever one you choose, you need to refer to your site from now on as either with or without the WWW. Believe it or not, Google sees these two URL’s as two different sites, so it is important you use the right URL whenever you are promoting your site. You don’t want people to start linking to you with a WWW when you don’t have WWW. That will dilute your link count in Google.
Say for example you are leaving a comment on someones blog. If you leave your URL without the WWW, Google will count this as one link to the non WWW site. Over time you might end up having 50 links pointing to the WWW site, and 50 links pointing to the non-WWW site, when what you should be having is 100 links pointing to the correct site.