Bide the Wiccan law ye must,
In perfect love, in perfect trust,
Eight words the Wiccan Rede fulfill:
An ye harm none, do what ye will.
Lest in thy self defence it be,
Ever mind the Rule of Three.
Follow this with mind and heart,
And merry ye meet and merry ye part.
The Rede is the center of all Wiccan ethics. It is the key to all other rules. Likened to the Golden Rule: "Do unto others, as you would have them do unto you." Unike other religions that have a list of rules, the Wicca have to take the Rede and interpete it for every situation. They have to constantly think about what is ethical or no.
To augment this Rede is the Law of Three: "Everything one does, for good or ill, comes back threefold."
Which is why Wiccans don't usually cast curses, as the curse would come back upon the caster.