I'm reading When, Why...If by Robin Wood. It's a book on magical ethics and I thought I'd finally read it as I've had it for years. She mentions the 3 fold law which states that what you do, good or bad, comes back to you 3 times over. In Wicca, in particular, this specific "law" is observed. The author treats it as a natural law of reality and notes that if you harm someone you need to make it up to them three times over in order to avoid the consequences. I've never been Wiccan, and I've never agreed with this kind of "law".
I definitely would agree that there are consequences for one's actions and sometimes those consequences aren't fun to deal with, but I've never really seen anyone get three worse or better what they did, and indeed if the 3 fold law is a natural law of the universe then who ever is enforcing that law is slacking off majorly (especially when it comes to politicians). Similarly I don't agree with the concept of harm none, and do what you will, because the reality is that life is just not that clear cut. Lets say you do magic to find a job. You are harming the chances of other people getting the job you get by using magic. You may not intend to harm them, but nonetheless by choosing to do magic to help yourself, in just about any circumstance there is a potential for harm. For that matter simply walking around or taking a breath is harming life you may not see or be aware of.
I don't advocate going out and harming people maliciously. And there are consequences for your actions and choices, including ones you may never be aware of. The ones you are aware of are the ones you have to take responsibility for. How you take responsibility for them is up to you and thus it can be valuable to put some time into creating your ethics, as well as exploring ethics in general. Nonetheless, it's also important to recognize that there's no deity or law that's going to hold you accountable or keep tally of your actions and who those actions have effected. The only being responsible for that tally is you, just as you are responsible for what you choose to do or not do about the consequences.
In my approach to magical work, I advocate not just being clear about your desired result, but also the consequences could occur. If you are comfortable with those consequences, then do your magical working. If you aren't comfortable, then its time to do some internal work and discover what is making you uncomfortable. You may end up choosing not to do the working and that's perfectly acceptable as well. Whatever choice you make should be one done with conscious awareness and intention and acceptance of your responsibility.