I had terrible dandruff before switching to no-poo methods. My hair was greasy, disgusting, and if I lifted the matted wad of fuzz that was my hair I could see thick white crust at the base. It was horrific.
Then I read up on no poo stuff, because apparently most shampoos have sulfates that strip natural oils from hair? Anyways, I had started out during winter break, so I had plenty of time to adjust, and let me tell you it is one hell of a transition phase (lasting about five-six weeks).
I went up to the store and bought some Apple Cider Vinegar and some baking soda, which was seriously super cheap! Less than a dollar for each! What you do is you put the baking soda in a cup, about half a cup, and then pour in a bit of water until it forms a paste, and then carefully rub that onto your scalp. Not the entire mane, mind you. Just the tippy top of your head.
Now, while this is sitting upon your dome, you wanna get out the apple cider vinegar (acv), and add one cup acv to one cup water, so that it's 50/50. Bring this appley wallpley concoction of cleansing with you up into your shower, and turn it on.
When showering, the first thing you want to do is obviously wash out the baking soda. Use warm-hot water at first, this will open up the pores on the scalp. Once it's out, turn off the water, and CAREFULLY, CARRRREFULLY pour the 50/50 mix of acv-water (which by now may be diluted quite a bit), evenly across your scalp, and wait about 3-15 minutes. The longer, the better. While you wait, wash the rest of your body off with soap or shave, or something to pass the time. ACV can condition hair, get rid of gunk, and just clean everything up. Also it's crammed full of vitamins and nutrients that's good for hair.
Now once your hair is dripping and smelling like an apple orchard, rinse it out with cool-cold water, slowly make it get colder and colder until you can't handle it any longer. This locks in the moisture, and closes up all the pores. If you can afterwards, just let it air-dry. I'm a guy with medium hair, so air drying is not really an issue for me.
Do this about once a week, and maybe try every other day with just water, eventually you'll get through.
As long as I don't get too sweaty, I could do this once a week and have clean, perfect hair all week long. Eventually you can try doing water-only washing, and acv-only washing.
Good luck, I hope I've helped a little bit. You don't have to do what I had done, it's just my 2 cents. As I said, I've got no dandruff at all anymore, and my head feels so wonderful.