E
Imma go on and slap you the with truth.
Whenever I play a ranked games some of my teammates always manage to
screw the match up. It has absolutely nothing to do with me.
Probably there's a good 20% of those games where you also did mistakes, may it be mechanical, wrong calls, or attitude amongst team members.
I was Diamond 3 at LoL Philippines, and then I moved to Oceania, and I got Plat 3 in 1 month of being level 30. (I started at Silver 3)
Elo hell is an excuse to blame your teammates for being stuck.
Watch this. (funny and real)
Once you've accepted some responsibility in the reason why you are in your rank, you can finally set that aside and focus on how to actually get better.
I'm not going to give you specific advice, but I will point you to the right directions.
There are 3 main skill dimensions in League :
Micro level (champion mechanics, team fights, instincts)
Macro level (long-term plans, action-reaction, map awareness)
Game Knowledge (champion abilities, map mechanics, respawn times)
In order to master the game, you have to master these 3 dimensions. Some people are good in one aspect, and some in the other. This explains why there are League coaches for worlds teams who are only silver/gold (needs citation), because they may be very good at the macro level and the game knowledge aspects, but they lack the mechanical skill to deliver their decisions well.
Try to assess yourself as to what aspect you need improvement in, and what do you need to focus on.
For myself, I main Thresh (he's the reason I jumped to Diamond), and in the hundreds of games with him, I admit that I still make mechanical mistakes and some wrong calls.
MAIN a champion and a role
Watch this vid by PhyLoL : Why Maining a Champion is one of the Best Ways to Get to Diamond 1
For me, this champion was Thresh. Mastering every little nitty bit of Thresh's mechanics, knowing all the possible matchups and how to approach them, knowing how I should build and how I should move depending on my ADC, and all those things.
I also mastered HOW MUCH I can trade. I know which trades I can win, and ones that I can lose, and all of this comes with mastering a single champion.
If you want to have fun, play. If you want to improve, study THEN play.
YouTube is the nesting grounds for a lot of coaches and general guides for LoL. I would suggest that you spend some of your time watching videos, opening yourself to knowledge you normally wouldn't think of but they're always there, and apply them to your games.
Some notable channels I personally like :
lastshadow9 - He provides THE BEST coaching advice I have ever witnessed. Period. See for yourself.
FoxDrop - Posts specific champion guides every now and then, watch them if you're interested to play that champion. He also posts champion guides for rank climbing - champs and builds that work generally against low elo players, but not as effective with Plat-Diamond players.
ScrapComputer - He posts heavy guides (some of them are even 1 hour long!) about aspects of the game. He digs into the details, and I recommend him very much.
PhyLol - Quite similar with FoxDrop. He also posts game breakdowns for Worlds games, so you can analyze what the pro players think and why they arrived at that specific situation.
Conclusion
I'm not the best (Diamond 3 back then in LoL PH, Plat 1 now in Lol OCE), but I dedicate my time to actually studying League, aside from just playing.
I do not go about and saying "I'm already Diamond. I'm the best in League. I can definitely own you ingame", but instead, I never stop learning, because when you stop studying, wherever you are, THAT is your personal Elo hell.
Some good reads :
Cloth5 Blogs - Provides really good insights and analyses on different aspects of League
The Bronze Escape - GETTING OUT OF ‘ELO HELL’
5 Key Mistakes that Low Elo players make