You will need:
Take a candle, preferably black or red. With a needle, write the name of the person you’re cursing. Take that same needle and burn the tip of it in the flame of another candle.
Once the tip is black, imagine the person you are cursing and stab the candle with their name in it. How many times you stab the candle is up to you. I usually choose 23, since it’s a number sacred to Eris.
When your candle is sufficiently stabbed, light it and focus on your curse’s intention. For instance, if someone has stolen from you, your intention could be that they would experience an equal theft.
Let the candle fully melt. You don’t want to reuse this one.
Harnessing Fire Magic (A Witch’s Guide to Elemental Magic)