How to get rid of dandruff permanently?

I have had it for a few months and i use head and shoulders every day. Sometimes my head itches so bad, i go take showers at like 3:00 in the morning. After i take the shower, it does not itch again for another 45 - 60 minutes.When i itch my hair 100`s of little white things come out. I just want to get rid of it for good. What should i do?