this will take a URL like http://hellojosh.com and redirect to http://www.hellojosh.com.
RewriteCond %{HTTP_HOST} ^hellojosh\.com$ [NC]
RewriteRule ^(.*)$ http://www.hellojosh.com/$1 [R=301,L]
This looks for a URL without the www and does a 301 redirect to the URL with www at the begginging of it.