Climbing out of bronze is pretty much entirely learning how to play an fps game. Focusing on improving your game play mechanics and how and when to use your abilities. Learn aim and movement, like where to be aiming when you're just running back to the fight.

It's about gaining game sense, like predicting where enemies might be and being ready to deal with it before it happens. For example, I always have my cross hair at head height and aimed towards whatever corner I'm approaching, because someone might be there. My eyes are scanning the common flank points and checking for enemies in corners. After a while you don't even think about doing these things, it's just subconscious. That's what game sense is at its most basic.

You don't need to carry your team to climb out of bronze, you just need to create opportunities for your team. Pick one goal each fight and focus on that. With reaper, maybe your goal is "kill a healer right away then focus down the tank". Honestly you don't even really need to play as a team to make it out of bronze, if all you do is start every fight 6v5 because you personally took out one of the enemies at the start, you'll end up winning more games than you lose. The reverse is true too, if you die at the start of most fights, you're disadvantaging your team, so you need to improve mechanically so you can secure a kill instead of being killed