Before applying the hair colour to your hair, it is always important to do a patch test.
Avoid shampooing
It is recommended to avoid shampooing before hair colouring as it will not help you protect the hair but rather wash away all the natural oil from your scalp.
Avoid chemicals
Keep in mind to choose non-ammonia hair dyes for your hair, as this will help you avoid all the chemicals present that might damage your hair.
Apply petroleum jelly
You can apply a thin layer of petroleum jelly on your hairline to avoid colour stains, and the dye will not reach your facial skin. This will also help to reduce skin irritation or itchiness.
Diluting colour
Mixing your dye with water or any other thermal oil will not help you make it darker or lighter; rather, the dye will lose its texture and become greasier.