The ranked struggle is real :/

Ahhh man. If you can picture this analogy you may understand. You are walking up a muddy hill, it is a long way, two steps up, and you slide back down.. No matter how hard you try, you always end up sliding down to where you started off. This is probably not true but it certainly feels that way. I have been working on my performance for some time now, I have found suitable champions for each role, I am never toxic, I always fill in ranked. Instead of complaining when others make mistakes ingame I look to see whether or not I can improve on something. Most games I do fairly well in the laning phase, however when it comes to late game I feel quite lost. Could anyone give me some pointers here?