Let’s make the example of this site :
1. www.kimbs.cn
2. kimbs.cn/
3. www.kimbs.cn/index.html
4. www.kimbs.cn/index.php
5. kimbs.cn/index.php
They are all the same in fact. We now redirect all of them to http://kimbs.cn in order to raise the PR(PageRange).
In .htaccess :
# url canonicalization
RewriteCond %{HTTP_HOST} ^www.kimbs.cn [NC]
RewriteRule ^(.*)$ http://kimbs.cn/$1 [L,R=301]
Easy, isn’t it? But also very important and please neglect it though minor issue.