I stopped using shampoo over six months ago, and now only "wash" my hair once a week. I used to have to wash it every day, or risk becoming a greasy mess. Needless to say, I'm happy with the change. So, what did going no poo mean for me?
I started out cold turkey--shampooed my hair one last time, and then just let it go a few days. Once it was REALLY in need of washing, I started with the no poo regimen: about 1 1/2T baking soda to 8 oz water, and 1 1/2T apple cider vinegar to 10 oz water. I applied the baking soda solution using a hair dye application bottle, so I could squirt the solution directly onto the roots of my hair. After getting in the shower and wetting my hair a bit, I'd scrub the solution into my scalp using my fingertips, and thoroughly rinse my hair. After that, I'd just dump the apple cider vinegar over my head, scrub with my fingertips, and rinse. I was immediately impressed; my hair was silky and clean and it was wonderful! However, it still became greasy after just a few days. While I never really experienced the dreaded "transition period," it did take me many months to get beyond having to wash my hair every 3 days or so.
My routine hasn't changed much. I now use 1T baking soda to 8 oz water, and 1T apple cider vinegar to 8 oz water. Note that the baking soda solution is kept in a bottle, so each individual application does not include the WHOLE 1T--it's actually a very small amount of baking soda being applied to my scalp. Occasionally I use lavender essential oil diluted in water as an extra nice-smelling rinse, used after the apple cider vinegar. Not only does it smell wonderful, it also makes my hair soft and silky.
On in-between days (that is, the other 5 or 6 days when I'm not using the BS/ACV), I just give my scalp a good scrub while I'm in the shower. If you have hard water, no poo may be a more difficult transition. I found that my hair responded very differently depending on where I was (I was semi-permanently living in two different places which apparently had different types of water). When I had to shower using hard water, I usually put a shower cap on to cover my hair on in-between days, since the hard water made my hair stiff and greasy-looking.
If you're just starting no poo and the BS/ACV combination doesn't seem to be working for you, don't despair! There are many, many combinations of washes/rinses for you to try. I recommend the no poo community on Livejournal (linked below) for specific information about different types of washes and rinses. For more general information about no poo, please see some of the other links I've listed below.
Useful No Poo Links
Wholesome Goodness: bye bye shampoo
The Boston Phoenix: The No Poo Do
Info about going shampoo free
Livejournal no poo community