It totally depends on where your from, whether you drive in sanded/salted roads, if you leave near a body of salt-water, how often you drive, how often you wash it
I personally wash my car about once a week and wax it nearly once every 1-3 months depending on the weather and whether or not it has been out in the Texas sun for a long time. A few good sites for washing or waxing info are
Meguiars car products help center
http://www.meguiars.com/faq/
A car detailing website
http://www.detailingworld.com/forum/index.php
Hopefully this helps
Meguiars car products help center
A car detailing website
http://www.detailingworld.com/forum/index.php
Hopefully this helps