use center tag

First ask questions

1. Have you designed page properly as per CS rules

2. Have you given proper widths to control

3. Have you done some basic study about page layout

If above is NO then just adding center tag will not help

Refer

http://www.wikihow.com/Center-Web-Page-Content-Using-CSS

http://stackoverflow.com/questions/10148661/how-to-center-a-webpage-in-css