Best way to improve in LOL?

I would say the best way to improve would be to watch your own replays, but not just for the sake of watching them, you have to know what you're looking for, so you need to inform yourself first, that's where Youtube guides like Mobalitycs and Skillcapped come in handy, besides watching your own replays and watching guides I would personally suggest to play a lot of games, have a champion pool of fewer than 4 champions (oneap, one ad, onetank, and one bruiser) and keep it simple, don't play overly mechanically complicated champions like Lee Sin or Nidalee. Hope that helps!