I have a very good idea so please listen!
Okay I've had problem in ranked where at least one lane that they called for fed and then I look at there other matches the problem is that they play a champion that they are new with in ranked... I mean common sense why would you play a champion your new with in ranked. So my idea is that to be able to play a champion in ranked you should at least have around 15 games with them in normal's, or have them at a mastery level of 2 or 3 as Whistle 48 Sho stated in the comments. I think this would be a very good idea. Please look into this Riot. :D