When you have dandruff you can wash your hair everyday to keep the dandruff out of your hair but when doing so be sure to use a medicated dandruff shampoo that will help keep the dandruff to a minimum.
The shampoo that you use when washing your hair with dandruff should contain ketoconazole, selenium sulfide, or zinc.
If you do wash your hair everyday when you have dandruff also use a dandruff conditioner along with the medicated dandruff shampoo to keep your hair from drying out and becoming brittle.
But you can also just wash your hair every other day which is also good enough to help keep dandruff out of your hair but washing your hair everyday is no problem as long as you use the dandruff conditioner.