When you have oily hair you should wash your hair more often and it's best to wash your hair as often as daily if your hair is really oily.
Washing your hair daily can remove the excess oil from your hair.
You can also use apple cider vinegar to help wash out the excess oil from your oily hair and wash your hair with the apple cider vinegar every few days.
Or you can also use some baking soda to scrub into your hair which is also a great natural way of getting rid of excess oil.
You can try using a shampoo for oily hair as well which helps to wash out more of the oily hair or even use some dawn dish soap.
My sister tried using dawn dish soap to wash her oily hair with and it worked to remove the oil from her hair as it works great for cleaning grease and oil off your hands as well.
After washing her hair with some dawn dish soap she then followed through with her shampoo for oily hair and washed her hair once again.
She washes her hair every few days with the dawn dish soap and on the other days she uses her shampoo for oily hair.