With all three kids one of the first rules we taught was "cords are no". I would be very careful to teach a clear and consistent boundary: just having your hand near a cord, brushing a cord while you were clearly going for something else, looking intently at cords, those were all fine. It was only reaching out to grab one that got a firm "cords are no" and separating them from the cord.

I don't have notes on when we started this with Lily or Anna, but with Nora it was just about when she turned 13m. Pretty quickly she got ~90% of the way there: I could let her play on the floor near my very cordy music setup and she would leave them alone, though if she was bored and the only things around were cords she might still go for them. By 15m (~7w after starting to teach) I rarely needed to intervene.

Toys on shelf: yes. Keyboard: yes. Drum pedals: yes. Cords: no.

Similarly, when she was ~14m she had been carrying things over to the bathtub and dropping them in. While not a safety issue, this isn't good for things that should stay dry. I decided to work with her on stopping: following her closely, and then when she was about to drop something in stopping her and firmly saying "no". I only had to do this twice before she went from doing this several times a day to almost never. A few more naturally spaced repetitions when she tried again a few weeks or months later and the boundary is clear. I still wouldn't hand her phone if the tub was full, but this isn't something she does anymore.

Other things we've taught this way with the older two have included street safety, not putting random things in the trash, not taking things out of the trash, not putting plastic bags on your head, "not food" for small objects, and staying out of our housemate's room. When I started drafting this post at 15m Nora was mostly not ready for these, though we had started working on streets and trash cans. At 19m she's good at not going into the street except we have to be careful at corners, she leaves the trash alone, and a "not food" on any individual small food-ambiguous object (ex: dry beans, food that fell on the floor a while ago and was missed) works well. Haven't started on plastic bags yet: we still keep those out of her environment. It seems to generally go best to introduce these one by one, and to have a clear idea in your head of the boundary you're teaching.

Unfortunately, this post makes crummy parenting advice because I think we may have atypically rule-oriented kids that this is an unusually good fit for. If this seems like something that might work for you and your kid, perhaps try it with a single rule, give it a few weeks of careful enforcement, and drop it for now if it seems like they're not getting it?