I was going to make a joke and say 'every day to keep manicurists in business'!! but seriously it depends on the condition of your nails and can really only be properly answered by actually seeing them.
You know you can also go to a salon just to have your nails polished. You don't have to have a full manicure every time :)
We have ladies who come to our salon every week just for a polish and then every so often they have a full manicure.