^ Well, depends on how your surrounding enviornment is.
If you live near an area with a lot of industrial fallout, acid rain, or near the ocean, once a month is perfect. Also it depends on if your car is garage kept or parked outside.
Don't wax it too much otherwise you'll get wax build up and then your paint will feel rough. I suggest using a rubbing compound or a clay bar once or twice a year. That will get all that "crap" out of your paint.