For greasy hair, don't wash your hair everyday cause you'll
stimulate the oil glands in your scalp and the oil production will
increase! 
Try washing it every
other day.
If you're caught with yucky greasy hair in the middle of the day
with no chance of washing it till hours later when you're home, a
temporary solution is to sprinkle talcum powder over your hair and
work it into the scalp. The powder kinda soaks up the oil and your
hair no longer feels greasy. But of course, you'd have to wash your
hair when you get home!
And use the correct shampoo for your hair!
