The biggest mistake new or lower elo players make when trying to climb is playing too many champions and/or lanes.
You need to specialize not just in a lane or a selection champs, but also in the type of champions. For instance, if you support main a Zyra support has totally difderent play style then a Thresh, who is again totally different from Jenna or Sona.
Pro players have something called muscle memory. This is something you develop when playing a certain style for a long time. So if you constantly switch between different support playing styles or between mid lane and adc, it is going to take you way longer to develop muscle memory my for a certain champion or playing style.
So choose 2 lanes you like the most and stick too champs that have similar playing styles. To be continued . . .
League Of Legends Guide 