Help with improvement at this game.

Im wanting to get good at this game. Ive been playing for about a year now and I've seen extremely little improvement other than me knowing more about the game. And I mean this to the point of when I first got ranked, I got ranked into Silver 5. Nearly a year later, and I'm still Silver 5, as I had to climb up from Bronze 5, which is what I got placed in this season. I one tricked Katarina since the start of Season 7, and she's the only one that I can even say that Im okay with. I decided I wanted to try out other champions when I made it back into Silver again, not be only good at one thing, improve how I am with the game in general. So for about 18 days now, Ive been trying out different champions. Yet its gotten to the point where I feel Im just getting worse. At first when I played them, I did decent, but nothing special. I though "Hey, Its fine, Ill improve eventually", yet now, Im only doing worse than I did before. I go into games, and 2 things happen. I either 1: Feed and lose, or 2: Feed and get carried. On the EXTREMELY rare occasion, Ill do well early game, but then Ill get constantly ganked by jungler, or whatever will roam to my lane, and I'll end up dying because I was too dumb to notice or stop it. I even tried to adopt the idea of "Well, losing will only show me my mistakes and what to do better next time", but that hasn't been happening either. Im making the same mistakes, and I KNOW some of the mistakes im making. Its gotten to the point where I can't even get tilted out of disappointment or getting upset at losing, because I expect it when I go into games. I've gotten to the point where I expect to feed and lose or feed and get carried. I have no clue what to do about it to not do either of those things. I guess all I'm asking is how to improve. I have no clue how to, if I did Id be doing that instead of typing and asking this. Please, help.