When should I try to give strategic advice, and how much should I say?

So I get the impression that my understanding of macrogame, while obviously nowhere near flawless, is substantially superior to that of at least 70% of everyone else in my MMR bracket (which is admittedly quite low, in part because my mechanics are just trash). Problem is, I don't know what people don't know and what is basic general knowledge. Despite not considering myself a particularly vocal player, in the past (and less often recently, but it still happens) I've been told I talk way too much and give too much unsolicited advice, and I know for myself personally I don't like being told something I already know. I certainly don't want to sound like I'm just bossing everyone around. But I feel like a lot more of my games could be won if a bit more basic strategy is employed. It doesn't help if I know what my teammates should be doing if they don't actually do it, and it seems way too late to say it after the fact, especially if it's late game and the blunder is severe enough that it results in a loss pretty much immediately.

I've been told not to make assumptions about what people do and don't know or will and won't do, but I can't just assume nothing. Assuming nothing means I'm playing extremely reactively, having to even react to what my own team is doing, which is equally if not more late than saying something after the fact, especially if I'm playing an initiator. Predictions are also based on assumptions. To be quite honest, if I assume nothing, the literal best play is to stand in base. Assuming everything seems to lead to the fewest confrontations, but also a lot of losses.

So, my question is, what assumptions are generally safe to make about what players know, and if it seems like someone doesn't know something that I know, how should I proceed? I can't be 100% sure about any assumption, but there must be some things that nearly every player knows.

EDIT: Oh wow it's getting even worse... there was a guy that didn't know what last hitting is. At. All. I even explained to him that he was missing cs because he was pushing so hard. He did not get it. Went completely over his head. I mean, I've had people who weren't last hitting because they just don't care and don't find it "fun," but they know what it is. This guy.. just didn't have the remotest understanding of the concept. No idea how to even explain it to him.