Alright maybe "good" leader was pushing it, because those kinds of things are exactly what good leaders do. But "great" leaders find ways to talk to teammates that keep them motivated and cooperative, keeping them focused on what needs to be done, so that they can do it and prevent dying in the future.
As for using pings to get people to listen: I make use of my minimap to spot incoming ganks for my allies, and then I go to that lane with my screen and ping danger on my ally's character then another danger ping in the direction the jungler will be coming from.
And as for using chat, it takes building up respect before things turn bad. If you're waiting to talk to people until you're already pissed that they made a stupid mistake then you're waiting too long. It's important to compliment things like saying, "good trade," or "nice escape" when something happens and they survive. Even simple things like asking how the lane is going before anything bad has happened. I do this regularly as a jungler, and you might be shocked at how positively my laners respond to seeing me show interest and support for them in their situation.
It's important to talk about what to do next time without throwing their ego under the bus (because lets be honest, once people think they are being blamed for things going wrong they stop listening and don't care what we have to say even if we have awesome suggestions for what to do next time).
Talking about the future and coordinating roams helps a bunch too, even if you don't end up making a play when you do roam. It's more about getting them to coordinate and cooperate as a team rather than about actually saving their lane if they have already started feeding.