I have a very simple method with two components:
1. Apple cider vinegar. I use about 3/4 cup+2 cups hot water for my thick, mid-back-length hair.
2. Lots of combing under hot running water with a ventilated brush (slots between bristles) or wide-toothed comb. This really helps to loosen gunk from the scalp and distribute oils down the hair shaft.
Put ACV in a container and set within reach until you're ready for it. Wet and comb hair until you feel it absolutely could not get any wetter. Add hot water to ACV. Hold some hair away from scalp with fingers, use other hand to pour a little ACV mixture (just pour until you feel it, then stop), and use fingers in hair to rub ACV into scalp. Continue until you've done your whole head. Comb without rinsing. Some oil will come off your hair onto the shower floor, so watch your step! Let ACV stay on hair for a while while you wash other body parts. (Do NOT shave! Vinegar really stings on freshly shaved skin!) Comb while rinsing. Hair will feel slippery, not squeaky-clean, when you're done. Style as desired (barrettes, etc.), squeeze with towel, and let air-dry.
In between washings, I rinse my hair with plain hot water every 2 or 3 days.
My transition period was about 5 months, during which I used ACV every other time and shampoo (followed by leave-in conditioner) in between. After two weeks, I had to switch to a milder shampoo and use less of it. Also, by then I was noticing that my hair didn't feel dirty as soon as usual, so I began washing less often. Finally, my hair couldn't tolerate shampoo anymore (it would turn into an itchy frizzball) so I quit using it altogether. By then I had decreased frequency of washing from every 2 days to every 10!
That was more than 2 years ago, and I've used shampoo only once since, when I got lead-based paint dust in my hair.
These days, I wash my hair when it starts to feel greasy and sticky, which is every 7-10 days in summer, every 10-14 in winter. It's much less frizzy than it used to be even when I was using a heavy conditioner. Instead of smelling like shampoo for 24 hours and then starting to smell funky, my hair smells fresh and clean all the time--even if I spend time in cigarette smoke, my hair just flings it off! (It does smell slightly like vinegar until it dries after washing and if it gets wet again in the next 36 hours or so.) It feels very silky and nice.
