There is no one rule or set of rules universal in Wicca. The Rede is the one that comes closest, but not all Wiccans follow it. The other "Rules"(they usually come in sets) are rules created by individaul Trads for their own Covens to follow. Being a solitary, It was necessary for me to create my own set of rules and my own Morality as I have no coven rules to follow.
How do you define your own morality and ethics?
Research, look up the most commonly used rules. Go over them one at a time. Do not say "This is a Wiccan rule, I am a Wiccan. Therefore I will follow this rule."
Instead, make a list,
Write down all the rules that you believe.
then take them one at a time and ask yourself, Why do I believe
this is a rule I should follow. Write down every thought no matter how trivial. Write an essay, if necessary.
Once you know why you believe what you believe,Its much easier to decide which rules you wish to abide by. Yes, I said wish.
You have free will.
Wicca is about self-responsibility. Even the Wiccan rede is to teach us responsibility for our own actions (or failure to act, for that matter.) It is a guideline,It is not an absolute. To take the Rede to a literal extreme is ridiculious.
As for the Law of return( or the three fold law)That too is a matter of self responibility. Karma is Not a punishment, Wiccan do not serve "The God With the Long White Beard" Think of Karma as a classroom. Too many F's and you have to repeat the class over and over and over til you get it right. After a while, if you're too thick headed and stobborn to catch on, the "lessons" may become more blatant and extreme til you get the point and can move on to the next lesson.
And sometimes,Its nothing that you've done, You're just getting a life Lesson that you need at this particular point in the evolution of your soul.
CM