The frequency of washing the hair depends on the hair type.If you have oily hair,then you should wash it with a mild shampoo every alternate day followed by proper conditioning.For oily hair choose shampoo that contains less of detergent.For dry hair,you can wash your hair two times a week.Also try alternating brands of shampoos after a few months.
Hope it helps.Take care and pls do keep me posted on how you are doing or if you have any additional queries.Warm regards.