Mindset.
Your mindset is the single most important thing if you're serious about improving.
A good mindset is:
In-game, stay calm and think by yourself.
After each game, point out your biggest mistake then think of a way to not repeat it.
Yes, you learn by making mistakes, go in there and make some mistakes happen, just remember to learn from them.
Unless you're challenger ranked 1 on the Korean server, it's impossible for you to say "I did no mistakes this game".
Arguing about mistakes in-game is about as counter productive as it can get. Focus on what to do next.
Elohell:
Bullsh*t.
Faker didn't become Faker "cuz lucky teammates".
Some games you will lose no matter what cuz unlucky team (accept it, it's part of the game).
Some games you will win no matter what cuz lucky team (just take it, compensates for the ones before).
But most games you can actually make a difference, that's where you make the magic happen, focus your attention there.
From game to game, the only constant variable is you (not the feeders, not the afk, not the flamer, YOU!). If you're in bronze, it's because you deserve to be. The sooner you face it, the sooner you can enter the proper mindset and start improving.
Also, this should be useful:
Do not type (use pings).
Objectives. Objectives. Objectives. (nexus > towers > farm > kills).
Watch educational content on YouTube (ex: PhRoXzOn (LeagueCraft 101), SoloRenektonOnly).
Truth is a lie, think by yourself.
Oh and almost forgot, git gud scrub <3.