Unless your hair is really dirty you can get by washing your hair once per week or twice per week at most.
I only wash my hair twice per week unless I'm feeling like my hair is more dirty then I wash the hair once per week.
Washing your hair too often can remove natural oils that keep your hairy healthy and shiny and also the hair can dry out and then you could have cracked split ends of your hair.
If you need to wash your hair more than once per week you should use moisturizing shampoo to wash out your hair and keep the hair moisturized.
You can also add coconut oil to your hair by warming some coconut oil up and then massaging the coconut oil into your hair and leave the coconut oil in your hair overnight.