A piece of string (preferably orange)
A black candle
This spell is best cast during a waning moon. While holding the string, take some time to think of the habit you want to change. Spend some time visualizing it - imagine how it feels to smoke a cigarette, or picture biting your nails. Imagine the craving, the desperate desire that comes when you try to break the habit. Now imagine the craving is passing into the string. Feel it leaving your body, and moving into the thread in your hands. When you feel the last of the craving leave your body, tie three firm knots into the string. Now the craving is trapped in that piece of string. To complete the spell, and to ensure that the craving can never return, light the candle and say the following:
I free myself now of this terrible addiction
No more am I plagued by this affliction
No more to suffer, now I am free
As I will it, so mote it be
Now burn the string in the flame of the candle. This ensures that the knots can never come undone, and that your craving will not return.