Tier and division are meaningless, that is just an indication of how well you are doing on a personal level against everyone else. The key is to improve your k/d/a, your objective clearing, and overall teamwork ability to carry at all positions (not just ad and ap carries). Your MMR is what matchmaking is about and that is a method of putting like-skilled together, regardless of division or tier. If you think that the Diamond player or Bronze player is all that different than you, you're wrong. The Diamond player not only plays like you but managed to win enough games on the way. Whereas the Bronze player hasn't yet won enough games.
If you don't realize this, you'll never improve. You need to have a carry attitude. If that means you see your adc is dope, then you protect him/her. If you see your jungler sucks, then you provide some support in any way you can. (sometimes a little goes a long way). A well-placed bush ward for 75 gold can score a double kill.
Try to anticipate the game progression and act proactively as if the game depends only on you.