Development and Improving Questions

So i recently decided that i want to "git gud", but dont know how to go about it. I'm mainly looking for improving myself as a player, not necessarily winning more games or anything like that.

Ideally id like to flex to any role, so one of my questions is what are some champions for each role that develop my skill and knowledge about the game? (develop mechanics, positioning, good micro and macro play, those sort of things.) I know people say helps you get in the habit of looking at the map, and thats the type of things im looking for. Champions like this are more important to me than if they are good or fun because they help me become a better player.

Aside from just playing, what are some other things i can do that will teach me important concepts about League? I know playing is probably the most effective way to learn and apply these things, but there are obviously going to be times when i get tilted, need a break, or just dont feel like playing. Its at these times that i feel like i could be doing something else to expand my knowledge about the game.

This is kind of a fresh start for me. Id like to forget everything i know about the game and start over, learning proper concepts and ideas along the way.