A couple things here. First, please oh please use your trinket. And don't just use it, use it somewhere the enemy is actually gonna run over it (river bushes and the bush by raptors gets so much action)
Also, ratings are determined based on your performance on that champ compared to other people in your elo playing that champ in that role
What this means is that getting a great KDA on someone like Quinn or yi is pointless, because just about anyone can get a great KDA on them currently. But that same score line on a soraka? Absolute S+.
I've found getting high rankings to be alot easier with off meta champs or in off meta roles (like a nasus jungle, or a bot lane teemo)