Hello ! You must first choose which version of your website you prefer: www.domain.com or domain.com
Once that is done, go to Google Webmaster Tools and create an account for each version, one for the www and one for the domain.com
Once created, tell GWT which is your favourite !
Then, you need to make a permanent rediretion 301 through your .htacess as follows to take out the www.:
RewriteEngine On
RewriteCond %{HTTP_HOST} ^www.midominio.com [NC]
RewriteRule ^(.*)$ http://midominio.com/$1 [L,R=301]
**Or Viceversa:**
RewriteEngine On
RewriteCond %{HTTP_HOST} ^midominio.com [NC]
RewriteRule ^(.*)$ http://www.midominio.com/$1 [L,R=301]
If you don't do this and both www and non www versions appear, then you have Duplicate Content !
