Little to no Impact on the Game

This is somewhat of a rant post but I honestly don't know how to win games anymore. I've tried different champions and roles but I can't get out of gold 5. Every game I play is decided by a teammates stupid decision in the early game. And every time this happens I'm "trapped" in a game that is unwinnable and not enjoyable to play. I'm losing more lp than I gain and I'm slowly going down from winning one game and losing one game.

Give tips on how to get of gold :')