I used about 250 grams of Ancient sunrise henna. For my liquid, I used a mildly acidic mix with a little extra water to make the mixture a little thinner. I left it out overnight.

I left in my hair for about three hours, probably a little more. I wrapped my toweled and plastic wrapped hair in my electric blanket and snuggled in it for a while. Then I washed it out with a little conditioner and shampoo.

I did this alone, but I'd probably get someone to help me in the future. I think I missed a few spots, as the front of my head is much less red than the back. It's a little darker than it appears in the picture, but that's about how red it is.

I'll definitely do this again! My hair feels so soft already!

Notes and References
Henna: https://www.mehandi.com/Mehandi-com-Ancient-Sunrise-Henna-for-Hair-s/121.htm
Don’t have fruit juice on hand? Keep some fruit acid powders in your cupboard.
Mildly acidic liquid: https://www.mehandi.com/Fruit-Acid-for-henna-dye-release-s/299.htm
More info on mildly acidic mixes: https://www.tapdancinglizard.com/henna-and-acidic-mixes/
Henna time and temperature: https://www.tapdancinglizard.com/mixing-and-testing-your-henna-mix pp. 10-13

Video How-To
Going red with henna: https://vimeo.com/manage/videos/739464950