Well good on you for asking.
Not knowing specifics, it's hard to give general advice. For instance, some champions can play well from behind and some are utterly useless. A Lee Sin who's behind can build kinda tanky and try to provide utility for his team by kicking enemies away from his carries or even getting picks by kicking a carry towards his teammates. He's better if he's ahead, but he CAN play from behind. Some champs like Nasus and almost always play from behind and become potent late due to scaling. Some, like most assassins... kinda don't have a use if they fall behind and can't assassinate people. Zed can't build tanky and matter much, after all.
So I ask you this OP... what roles and champions do you play? It will help people give you better advice overall.
As basic, general advice I'd say to lean away from high risk/high reward champions if this is a problem you want to improve on. Stay away from the champs that can't do much if they fall behind and pick up champs that have potent mid-late game power... even if they ARE behind. Champs like Jax or Master Yi are simple to use and scale really well. Or if you don't want to go with a champ like that, get into mages with good, strong waveclear and CC. Or maybe a big, meaty champ like Warwick that can build tanky and still do decent damage... as well as picking people off with his ult.
Play the game to CS and get objectives, not get kills... and avoid taking risks if you can. Eventually you'll need to get bolder and make plays to get ahead, but in bronze... just farming better and being the guy who gets dragon or a tower instead of chasing a low health enemy after a fight is all you really need to do.