Finding strong overall game champions

I am getting really tired of having my games go from 10/4 one game to 3/12 the next because i just play a random champ every game. Can someone please help me chose a main role to play for each lane in ranked 5's so i can have some consistency with my k/d based off of working more on certain champions instead of my usual random picks. I would like to start getting better with one main role for each lane and work from there. Any help is greatly appreciated.