I am a Platinum V midlaner looking to get better at the game.

I mainly play Vel'koz but I would like to know what I can do to improve my game. I do realize that my farming is sub optimal and I could react more quickly at times, but, I'm not sure that those are not the only issues. I really love playing this game and would like to play at the highest level of play. If you have any pointers or tips please respond. Thank you for your time and have a nice day! :D