WHAT ARE THE ETHICS OF WITCHCRAFT?
When you say, "An it harmed none", that is exactly what it means in your work. It is important to say this, because you are therefore asking for an outcome that will not harm anyone. If you ask that no one gets harmed in the process, you are stating that your intention must be granted only under these terms. If it is not possible that no one gets harmed, then it will not be a fulfilled spell. With practice, you will get in the habit of saying "harm to none" readily. I think of my family especially, and do not want them to come to any harm because of a spell I might cast. This fact alone may make you very careful of always saying it.
If you forget, just say it out loud afterwards and visualize
"Harm Coming to No One"
A basic rule of Witchcraft, for me as a Wiccan,
is that I cast spells for people and not on them.
Unless there are very special circumstances,
I never cast spells for anyone without their permission.
Interfering with someone else's karma affects your karma too.
This might be something you have to straighten
out with that person in your next lifetime.
Remember what you learned in Physics:
For every action there is an equal and opposite reaction.
Magic is the manipulation of energy, so this definitely applies. - Ishtar
WHY DO I HAVE TO SAY 'WITH HARM TO NONE'?
For one thing, "With harm to None", protects anyone who may get in the path of one of your spells, even your own family members.
This is very necessary, to me. - Ishtar