I wish there was some easy way to know for sure what to do. But in order to do that, we would have to have a list of approved and forbidden behaviors. We don't, because everything is a special case, and such a list would not be flexible enough for real life.
So we go with the Rede, and try to do make the right choice. We have to think about what we are doing, and listen to our instincts, and to our inner voice, and do what we think is best in any circumstance.
No, it isn't easy. But then, this isn't an easy path.
But it isn't as hard as all that, either! You know when you harm someone on purpose, out of anger or jealousy or fear or hatred or whatever. And when you do, there is a little voice inside that tells you you should not be doing this, isn't there? And afterwards, you don't like yourself as well, do you? Well, that's the secret. If you do something you should not be doing, you know it! Don't do it. And if you have done it, then go to the person you have harmed, apologize, and ask what you can do to set things right.
If the person you have hurt is yourself, still apologize, and ask what can be done to make it better. You may feel a bit silly talking to yourself, but it does help!
It's my opinion that if you can't respect yourself, and trust yourself, then who can you respect and trust? Treat yourself exactly as well as you would treat a friend you admire and respect; no better and no worse. Then you can get a realistic view things.
So do your honest best. And don't beat yourself up if you mess up. This isn't one of the religions that expects us to be perfect, after all! We all goof up all the time, but's it's OK. We have lifetimes to get it right.
There are no guarantees, but there is no judgment either, so go with your instincts, as I've said, and pay attention to how you feel about things, and you'll do alright.