All i did was buy an ethernet !
I wanna make this post because it worked for me and i am sure it can help many people. Now i know it's pretty basic info but there are people unaware of it so i feel like it must be told.
I used to get INSANE lag spikes while playing the game. My champion couldn't move and i kept dying because of that. Tha lag would last long and ruined my whole game. I tried it all, power settings, graphic settings, i closed every single programm running on my pc, even put lol in high priority from my task manager, nothing worked. The lag was REAL !!!
I called comcast which is my provider, they asked me to run a speed test.
I had 2.9 mb/s download speed, normal ping and some ridiculously low upload speed. I was connected with wifi. The customer service employee asked me to use an ethernet cable and run these tests again. After i did the downlowad speed went to 29 mb/s ! Yes it got 10 times higher instantly just by plugging the ethernet instead of wifi. The ping got even smaller and the upload speed went tremendously up!
Ever since i did that, i have NEVER lagged again. Not a single time in 3 weeks !!! Amazing change... I went from unplayable to never lag!!.
I had stopped playing ranked games because i felt bad for my teammates, that's how bad it was. I was even considering to stop playing the game until the ethernet saved me!!!
You should try it and see the lags disappear!