How to gain elo - 3 rules.
Rule #1: Stop blaming your team.
You don't like the way that person on your team is playing? You don't like the items he's building or the champion he picked? Well, you're just going to have to deal with it.
Here's the thing, when you play ranked, you're gonna get matched up with 4 random people, and you're going to play against 5 random people.
All of these people are going to play the game how they want. Depending on how they play, it may impact whether or not your nexus is the one that explodes. There's generally not a point in explaining things to other players, especially ones who are only going to spew toxic vile back into your chat logs. But also because you probably won't ever run into them again unless you're in high diamond/masters.
The only common factor in all your games is you. You can complain about your teammates doing stupid shit all the time but if you're in the same rating as them it means you are doing the same thing. As long as you're consistently making the right decisions, playing strong picks, and generally doing better than your counterparts you will win games more often than not and gain ranks.
There is no elo hell, there's tons of crybabies who'll probably post in this thread about how it is real and they wouldn't be bronze if they didn't have decent teams. Trust me, if you're in bronze you are terrible at this game and belong in bronze. Realizing that is half the battle.
Rule #2: Have a small champion pool.
Don't be that guy who plays a different champion every game. Sure, maybe it'll work out fine, maybe you'll just have a 50% winrate maybe you're happy staying in gold whatever. But if you're serious about gaining rating you pick like 2-3 champions and ONLY play those champions.
Only play the champions that you are confident you can hard carry games with. No I'm not saying only play carry champs what I'm saying is that you can carry from any role, I've seen thresh mains and bard mains hard carry games and don't tell me it only works in plat+ because i've seen it in bronze.
Having a small champion pool means you can have a good understanding of most matchups and interactions between your champs and the rest of the played champions within a meta. Knowing when you can engage/whether or not you can make that pick/how quickly you can 2 man baron down, these things are very important. Make sure you are prepared for a lot of situations.
Rule #3: Take breaks.
Not only just because you lost and are tilted or whatever. After each game you should take some time to think about why you won or lost. I've lost so many games and it was just abundantly clear it was my fault. I've lost games where i was doing extremely well and even then I'm left thinking "what could i have done better?" or "how could i have won that game?"
Don't bother thinking "well my team was just straight up worse than the other team, so there's nothing i could have done to win that game". If your goal is to gain rating then you should be trying to win every single game, including the hard ones. Winning the 'impossble game' where everyone on your team feeds their asses off not only feels amazing but is much more impressive than stomping the other team into a 20 minute surrender.
Almost every single game is winnable regardless of how 'bad' your team is. It takes only a couple of minor mistakes on the other side (or just crazy good plays from your side) to take baron and start the comeback. Think about how you could have set the wheels in motion to make that happen.
Taking time to just think after your games can go a long way in improving your play.