In the Joomla backend, go to the Plugin Manager and open a plugin called User - Profile. This contains some additional fields that will appear on the default Joomla registration form. The fields it provides are:
- Address 1
- Address 2
- City
- Region
- Country
- Postal / ZIP Code
- Phone
- Web site
- Favourite Book
- About Me
- Terms of Service
- Select TOS Article
- Date of Birth
Select which fields you wish to use and enable the plugin.
Hope this helps