I put my powder (maybe 1/3 cup of powder or even less) in an old stocking. I add warm water in a cup with the stocking in it and squeeze and squeeze. Because my curly hair holds the teeny tiny grains from the shikakai and I can't brush my curls once dry, this makes me happier. I then put the liquid in the same squirt bottle as I will put my acid rinse and squirt it all over. In the shower on wet hair (a choice) I massage the scalp and behind the ears lol and rinse. I also rinse out that stocking for use again ;)
I do use my ACV (apple cider vinegar) acid rinse after because my hair loves it!!!! Shikakai alone doesn't need an acid rinse though, it is already ph balanced for hair and scalp.
Some people add a little Amla for shine or reetha/soapnuts for extra cleansing in their shikakai wash.
I also detangle with a wide tooth comb with the ACV soaked hair.
I do the same after henna. I mermaid rinse soaking in the tub for some time getting as much henna out, then standing shower rinse again with water. I only use water to rinse out my henna. I add my ACV mix and verrrrryyyy gently detangle with a wide toothed comb with ACV still in. Then rinse again, and repeat as needed.
I plop to dry after that.
Basically, I wash with shikakai or use henna as a wash since I'm only washing once every 3 weeks.
I do have a low poo on hand for hairdresser visits though ;)