There are so many aspects in this game that have to be taken into mind when asking this question. How good is their CS, How well do they rotate, how good is their macro game? I'm trying to climb right now and I'm trying to take every measure possible to make myself a good player. Tell me what you think, how does someone "git gud"?
It's a combination of things:
There's probably more, but that's the broadest categories I could think of off the top of my head.
Common sense and being self-aware are the biggest things to help you improve in league. A lot of mechanics or certain rune pages/item builds etc. doesn't really matter. The biggest reason people fail in this game is cause they lack common sense or they refuse to admit to messing up and continue to do so because of that
What makes a player good is the ability to fight against luck.
Even if you are skilled you need to know how to play in every unlucky match and try to avoid mistakes made by luck, that way if you make a mistake is because you thought about it before doing it and not because bad mechanics or knowledge.
The most important thing is game knowledge hands down. You can have bad mechanics and still make it to Master tier. There are several streamers who have done it and they admit they don't have good mechanics. Being able to last hit, wave control, know champion power spikes, etc. gives you a big advantage in any game.
The second most important is probably map awareness and third actual champion mechanics.
