User blog comment:Mineko Charat Lucky/What makes Platinum players different from Gold, and Diamond to Platinum?/@comment-24013328-20131027133807

I'm not a Platinum or Diamond player, but I think I may have something to offer, though it isn't by any stretch my own original thought. According to Phreak, the biggest difference between Bronze/Silver/Gold and Platinum is mechanical skill: the ability to last-hit, dodge skillshots, etc. The difference between Platinum and Diamond tends to be decision-making: when to take objetives, when to push hard or freeze the lane, when to gank where, things like that. Then the difference between Diamond 1 and Challenger tends to come down to how well individual players are able to become a team on a moment's notice, so to speak. But remember, this is just one player's take on the matter, being a Shoutcaster for Riot doesn't make him God.

TL;DR: The way to get above Gold is to just play a lot and learn what you think you're missing; the decision-making aspect of the game. Get a feel for when to do what.

Personal note: I find that the best way to find one's own mistakes is to re-watch one's self doing a task. Go back and watch the games you play and think about what you do and why you did it, it could shed some light on your mistakes.