Regarding the earlier discussion concerning climbing the ladder in ranked I just want to point out that most high level players in ranked focus on 1 to two roles. If you can play every role properly enough then you really don't belong amongst the lower/average elos. Team comp tends to not really matter until higher gold because proper mechanics and decision making can carry you up until then. The UNSWlol lecture guy played AD soraka and would still win games.
Last season I flopped around in silver trying to be a jack of all trades until I focused my champion pool to just Jax and Tryn top with a Leona support. Managed to get to Gold 1 in a week doing mostly just those three and my match history was littered with isolated losses when I tried running unfamiliar champs.
yeah decision making coupled with execution is the biggest thing if you are trying to get out of silver i think