Why am I so HORRIBLE

I've been playing league for a while now, i'm level 31, but I still can't get any better at the game. I've tried tons of champions and the only one I seem to be atleast 'ok' with is xin zhao. (Except for that one game where I was like 0/12). You can check out my match history ,see what I mean (ignore jinx games my brother played her only). If you have any suggestions at how to improve, please answer this post.
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