irst, you must clean or wash the skin / area where you want to apply the pattern. Mehndi is generally applied to the hands and the feet but can also be imprinted on the shoulders etc.
If you are worried about making a mistake you can make a light first trace of the pattern / design on the skin. Mehndi is painted on with a special instrument or henna cone, and the design patterns should be drawn from the outside to the inside.
If you want mehndi pattern or design thin lines, try drawing it with a toothpick or matches.
After the Mehndi tattoo application is completed, your applied areas must be away from water for about 4 to 6 hours, as the skin require some time to absorb the henna paste and getting dark.
Now, once you are not happy with the design pattern, it can be washed off within that period with soap and hot water.