Honestly, I was in Bronze 5 the whole third season. I went into my placements all excited, won 7/10 games and was placed in Bronze 5. This was due to how low my MMR was, which I could see is happening to a lot of Bronze people. At the moment I'm Bronze 1 and hoping to Reach Gold this season. One main problem I realized I had, was co-operating with my team. Kills are good to have under your belt, but objectives are a lot better. Dragon gives gold to the whole team, Turrets give gold & applies a lot of pressure. Split pushing at the correct time can turn a whole game around, perhaps the most fed person on the enemy team goes to fight you, but your team fights a 4v4 and wins. Baron is also huge obviously, a tremendous buff to the whole time which gives an edge in team fights. Sometimes you have to give kills over to help your team catch up if they're behind. And one main rule to follow, is don't rage at anyone on your team.