Take a plastic bowl and pour in it henna quantity according to the length of your hair. Mix it with lemon juice or vinegar. This liquid is acidic and brings out the color of the henna. Stir the henna well to form a consistent paste with no lumps. Cover the bowl and leave it overnight so that henna gets time to bleed.
During this soak time, you can add oils to nourish the hair and dyes to alter the henna color. If you want a brownish shade, you can add in indigo to the soaked henna.
You should do a patch test on strands of hair from any haircut or on a small hidden portion of your head. This will give you an idea of the color you want. It will give you an idea of the time the henna needs to dye the hair as well.
Henna is ready to be applied when its surface turns brown. Put petroleum jelly or cotton strips on your forehead to prevent it from getting painted with henna. Part your hair into sections.
Wear gloves on your hands and start applying the henna on to the hair, from the scalp to the tips of the hair. Cover your hair well with the henna paste. Once done, cover your head with a plastic wrap that will retain moisture and create a medium for the henna to develop color
When the time of the henna you determined in the patch test is over, wash it off with warm water. Condition your hair well to bring out the color.