-Play easy champions that also have high impact. (Nasus, Malzahar, Yorick, Janna)
-Play the role that is easiest to you.
-Play that same role every game.
-Don't play different champions every game.
-Pick 1-3 champions and play NOTHING but those champions in every game.
If you want to get better results, you have to be disciplined enough to start playing for consistency rather than fun.
Once you do those things, you can be more easily be coached by a better player if you get stuck and still don't know what you are doing wrong.