I don't really use henna anymore because I hate the mess. I just used it because I bought it and did not want to waste my money. I just use cassia powder or just store brand henna products that are labeled as neutral (i.e surya powder, light mountain henna neutral, etc.). Some people don't like these, but they work just as well as the henna that I used for about a month.
I have a 1 oz scoop and I use about 3 of those scoops of the powder, 1 cup (about 6 oz.) of plain yogurt, about 2 oz. of boiling water, some oil (I am using amla right now and I don't measure it. I just pour some in).
I use it weekly of every other week if I am busy. I try not to go more than 2 weeks, although I am sure I don't need to do it that often. I just like the treatments. I am relaxed and I do this treatment every week except relaxer week.
I used to put it on my wet hair, but I have found that it saves time to do it this way:
-on Saturday or Sunday I put the mixture on my dry hair.
-I put on a plastic cap and sit under the dryer for 20 min.
-Then I workout for 40-60 min with the mixture still on.
-Then I rinse it which is another process:
I rinse as much as possible with plain water. Then I use Johnson's Baby shampoo detangling for 3 sudsings using a detangling comb while the suds are in. If I don't use the comb it does not rinse, as well. Then I use my moisturizinf shampoo for a 4th sudsing. I guess you can skip that step. I just do that because my Roux Porsity Control shampoo makes my hair feel so good.
-Then I apply some Motions Moisture plus and sit under the dryer with a plastic cap for 20 min.
-After that is rinsed, I style as usual. I thought my hair was dry after the 1st time I tried it, but it was not. It was just stronger. I never had any dryness problems.