The following are some steps you can follow to ensure a nice stain:
Henna looks different on everyone. Body chemistry, temperature and location on the body have a lot to do with how dark the stain will be. Thicker skin on the hands and feet stains much darker than the softer skin on the upper arm or back. Henna stains are darkest during the first 7-10 days, then it starts to fade.
LEAVE PASTE ON AS LONG AS POSSIBLE
At least 5-6 hours or more. Leave paste on overnight for best results. The longer the paste stays on the skin, the darker the stain will be.
You can use lemon juice or olive oil to remove the paste. You can also gently scrape the paste off or let it fall off naturally. DO NOT USE WATER to remove paste. Try to keep the area dry for the first full day after you remove the paste as water will stop the darkening processes of your henna stain. Avoid cleaning products and chlorinated water. If you must get the area wet cover the henna design with lip balm, or olive oil. Reapply frequently. Do not use exfoliating scrubs, luffas or anything else intended to remove the dead surface skin. That's where the henna is! Henna stains take 48 hours to reach color peak.