I qualified Bronze 1, got demoted twice to bronze 3, and pushed up to Silver 1 (now silver 2, my fault) within this season alone. It didn't happen because all of a sudden my teammates started playing better and made better decisions.
If you're in Bronze, your opponents suck. Your teammates suck. Which means if you're decent, you put your time in a gigantic advantage. Not every game is winnable. Some people will flat out ruin a game for you, if you think this changes once you leave bronze you'd be saddened to hear that's not true. It's the very nature of this game that someone did something you didn't want them to and will cost you the game for their idiotic mistake. It's the very nature of this game that you yourself will do something really stupid despite what the team might have wanted and you'll lose them their game. Ultimately: there are things you can personally achieve without anyones help to make the odds of you winning a lot higher.
1) CSing better and understanding trades. The higher your CS and better you're able to trade, the more gold you have experience you'll have, and less often your opponent will be benefiting in lane.
2) Buy a shit ton of wards. The average bronze player buys less than 1 vision ward per game and less than 3 stealth wards per game. Want to be way above average? Increase those statistics. Buy wards almost everytime you can outside of your first rush item, and if there's ever a time your vision ward gets destroyed, buy one on your next back. Vision is OP as shit.
3) Stick with a few champions and only a few roles. If you keep chasing FOTM builds and lanes and whatnot, you keep not building upon what you've already learned. It's more valuable to be the best lee sin jungle in bronze league than be an average lee sin, average evelynn, and oh you dabble with Ezreal adc but sometimes you twitch but then again Jinx is fun yadda yadda yadda. State your 3 preferentials and let the team know in a nice way you and them will be better off if you're playing that role.
4) Don't die. Essentially every death in league is your fault. Not your team's for baiting you into a 1v5, not "oh well their jungle is camping me", no fuck that. Do what you need to do to not die. ALMOST every death is avoidable in league, save your escapes wisely, make less mistakes. There's a reason LCS games end with KD scores that don't make up 1/4th of how many kills happen in public ranked games.
5) Reflect upon what you coulda done better that round. Who gives a shit that Nasus only had 45 stacks at the end of the game top lane, maybe you shouldn't have picked Vayne if they already locked in caitlyn. Maybe you could have CS'd better. Maybe you didn't ward right. Maybe your positioning was off in one team fight which helped them get a 3 for 1 + a turret. Maybe you didn't call for a rotation to take an objective enough. Ultimately: you wont have to play with them again, but you have to play with yourself every match.
Do that shit, watch yourself grow. Don't, I'll see you again in a year where you're still bronze and the friends around you are platinum.