Mastering my favorite champion

Basically, I've discovered Irelia a while ago. I've learned item sets, combos and everything. Done some AD and TANK runes, depending on my matchup and learned to adapt items depending on my matchup. I still lose. What else can I do? Where can I improve? Also, what other champions do you recommend? I've wanted to buy Renekton for a while. If you got any tips for me to improve even more at my champions, please leave a comment.
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