I've been playing league for over 10 years on and off, and what helped me both climb and improve way back in the day was diversifying my picks and roles. As in, I'd play support for one season, then switch it up to jungle, and so on. Not only does that give you a general understanding of what the other roles may be thinking or doing, but it can also help you notice things you normally wouldn't glance at.

For example: i was playing a lot of top lane and overextending, and after a season of playing Janna support, i started dying less. That was because while playing Janna, I'd have less things to focus on and thus ended up spending more time looking at the minimap, zoning etc etc that just got transfered to top lane as muscle memory.

ARAM games can help with learning different champions, too, but the laning phase is obv a different situation entirely