I've been experimenting with it for almost a year. If you research it you won't find 2 people who suggest the same recipe, and all the people doing the suggesting are bloggers (aka random people on the internet, like me :p). With all that in mind I still tried it because I don't like the commercial shampoo with all its synthetic chemicals that totally strip my hair of its natural oils. Before I go into my journey, I want to say that I think different ratios and mixtures work better for different people/hair types. So with that in mind I have dark brown hair which is also straight, thin, and fine. I used to use commercial shampoo and conditioner every day, and went "cold turkey" when I swapped to the baking soda/apple cider vinegar.
Here's basically my journey:
Phase1: I started off with 1 tbsp baking soda to 1 cup of water, and 1 cup apple cider vinegar to 1 cup water. I poured about half the baking soda mixture over my scalp (not through the entirety of my hair), rubbed my hair around on my scalp, and then rinsed it out. Then I sprayed the apple cider vinegar mixture all over my scalp and hair, massaged the ends and my scalp a bit, then let it sit while I lather up and do the rest of my routine, finally rinse it out. I had to play around a bit to get to this final routine, but this is what worked for my transition phase. Took me about 6 weeks to totally transition and I was washing my hair every 2-3 days. During transition I was a bit more oily than normal, but putting your hair in a pony tail helps a lot to hide the oily days.
Phase2: A few months later I started to realize that I was losing a lot of hair in the shower and finding a lot of stray strands of my hair on my clothes. I was slightly alarmed but didn't want to switch back to the shampoo/conditioner so I did a bunch MORE research and found that people were saying baking soda is not actually good for your hair because of how basic it is (basic as in PH level). Shampoo has the same deal, its basic, and that's supposedly bad for your hair because your hair/scalp is naturally acidic. So, I basically stopped using baking soda and started just rinsing out my hair every couple days then using the apple cider vinegar (it helps me comb my hair out post shower). Since I had already transitioned from washing every day, this was mostly enough. I do get some build up though, so I will use the baking soda about once a week and also use a little bit of shampoo maybe once a month. My hair stopped falling out and its been feeling pretty silky and strong. Lastly, I found that getting the boar bristle brush and brushing through the hair twice a day really helps with reducing the oil buildup since the oil becomes more spread out across my hair.