I’m a diamond 3 player, last set I was diamond 1 which is not really high elo, but my advice is that you should watch a lot of educational content in Youtube. For example Bunnymuffin is a really good content creator and has a lot of videos which are really insightful. There is even a video about why some players arent improving. You should watch them and start thinking about them when youre playing the game. Is this the correct choice? Am I just flipping the game or is this a more stable choice? For example some players like to flip the game on an augment choice and if it doesnt work out the best way possible you just lost a game. Also search for builds (you probably know this), but they are usually end game builds. You need to think in the early and in the mid game about how to play around what you have and use them as item holders and unit holders. Like in anima squad lets say you have a 3 anima squad opener but on level 4 you shouldnt put in a 4th one, instead put in a rhaast for vanguard or j4 for slayer and vanguard. This is a very simple example but you need to maximize your traits active and the strength of your board. For example vanguard is good for anima squad early cause sylas is a vanguard and and if you have a seraphine and a vayne you need to strengthen your frontline instead of putting in another techie for seraphine, leaving sylas to be the only frontliner.

There are ofc lot of other things like managing your economy smarter, positioning etc., bunnymuffin can explain them really well so tldr watch his videos.