Shave or wax all the hair off of the skin where the henna is to be applied. Hair will prevent the henna from coming in full contact with the skin and will result in a lighter color stain on your skin. Uneven color in the design is also caused by the hair blocking the absorption of the color.
Add essential oils to the henna that contains hennotannic acid. Some oils that are known to be effective include tea tree, lavender, cajeput and ravensara. While these oils are not likely to cause skin irritation, as with any product added to the skin, it is a possibility. Perform a test on a small area of your skin ahead of time to ensure you will not have a reaction to the oil you wish to use.
Apply the henna in a warm environment. In summer, the henna will naturally become darker as it responds to the heat. In winter, the areas henna is applied to should be wrapped and the room kept warm.
Leave the henna on for a minimum of 2 hours. The longer you leave it on, the better the color will develop and become darker. If possible, leave it on overnight. Apply a sealer mixture, the most common being lemon juice and sugar, and loosely wrap the area to keep the henna stuck to the skin while you sleep.
Wash the henna away with water but do not scrub or pick off the pieces. This will exfoliate the skin which actually removes the color. Picking them off will actually be painful and make your skin sore, especially if you used a sealing agent to keep them on during sleep. It is expected that some pieces will harden and fall off of your skin as the paste dries and this is not a problem.