I had started ranked games at 230 wins or so, had a decent W:L even in the beginning, but in some cases I was just lucky to have good teammates giving me advice. Then I tried playing all roles:
- practice 60~80 cs @ 10mins for solo top/mid
- take jungle times and learn to roam/gank
- learn how/when to initiate teamfights as tank
- L2ward and help your lane partner farm as a support
If you get a grasp on that, all that's left is teamplay...unfortunately, it can't be learned since it takes more than 1 person to make a team
