I want to get better at League in the new season, but I need some guidance!

(Originally posted in Misc. Moved to Gameplay for hopefully more views. I think I should have posted this here to begin with.)

Hello all, I made this topic in an effort to get some information on hopefully making myself better at League and maybe some day start using my Youtube channel to post ranked gameplay videos (Long time off) but I really need some guidance on where to start. Basically what I'm looking for is direction. I made it to Platinum about 3 times last season, but ended up finishing in Gold II. I'd consider myself an "average" player (whatever that means) and know the basics of the game. I have a handful of champions I know how to play well and I'm well rounded in about every role except for ADC.

I've often heard the best way to get better at League is to record your games and watch them to see where you make mistakes. Then identify how to fix those mistakes so you don't continue to repeat them. I'm hoping somebody can point me in the right direction of a good starting point to start recording my games. What do you all use? Any specific application? I've noticed OP.GG.NA (I use this to track a lot of my statistics) has some sort of recording feature, but I've never been able to figure it out. Any suggestions on what to use?

Any other things worth mentioning to practice? I've heard practicing CSing in custom matches is good. I feel like I have a good grasp on that already, but you can look up my stats and see if my creep scores are too low.

Any guidance is much appreciated! I'm really specifically looking for ideas on how to record my games effectively, but any other suggestions are welcomed.

Thank you to anybody who takes the time to read this. Sorry for the text wall.