Before you apply, make sure you have two plastic gloves and some vaseline. Apply the vaseline generously all over your hands, upper forearms, and neck. Also apply some next to your hairline on your forehead, and around your face. Apply a good amount to your ears, and around/behind the ears as well. Be sure to apply a lot on the BACK of your neck since that's where the henna will most likely touch your skin once it is applied on your hair.
Slathering Vaseline all over your skin may seem gross, but henna is also a natural skin tattoo, so if it touches your skin, it will color it an orangish-brown tone. Vaseline helps avoid this, along with the plastic gloves. Do NOT apply henna without plastic gloves.