First of all, don't listen to people that write half a paragraph to try and tell you how to play this game. Since we cannot actually see you play, our commentary should focus on how you can improve your game-play, not actually "how you should play".
I sometimes give people a "random pool of tips" and classify it as such. It won't teach you how to play, but might give you a few ideas. And then I always back that up with "the main thing is simply keep on playing and for god's sake analyse your games to see what you did wrong". I think the tip you could use the most (considering what you already stated) is to keep up-to-date with the meta on probuilds.net. Pick your role, pick your champ pool, and then look up which one's the most viable. You might even consider taking the highest-winrate champions and learning those. Then you can set up your runes, masteries and builds based on how the top-tier of soloQ is doing it right now. All that's left then is to play the champion, analyse your games and if you get stuck, look up a recent top-tier game featuring the match-up you are stuck on.
Time for a side-note, feel free to skip it. Note how this does not teach you how to play, it rather suggests how you should start working on your game-play on your own. "Work on your awareness - it's probably still bad" or "Work on your decisions/mechanics/anything else completely abstract that will always be appropriately bad based on what someone's MMR is" simply does not teach you anything. I could say "Don't die pointlessly" to you or myself because we both often die pointlessly in our games, but that does not help you improve your own game-play and as such is not helpful at all.
Now, to actually go into specifically what you said about KDA and win-rate, let me express my opinion very clearly. Anything you do correctly or poorly - mechanics, warding, awareness, decision-making based on the aforementioned, etc. - will directly influence your KDA. So, even though "This game is not a COD team deathmatch where the most kills wins", your KDA is a surprisingly accurate indicator of your performance. Your KDA will usually reflect your expected win-rate, which means if your win-rate is 45% but your KDA is 7/5/7, you are simply expected to slowly go towards a win rate of say, 55% (read: "above 50%, but not amazing enough to be 60%+").
So, just keep playing, start/continue analyzing, hopefully benefit from my tips, for instance about using probuilds.net and perhaps tournament/challenger streams to educate yourself about the current meta. Stop worrying about your current win-rate unless you have played over 200 games already. If your KDA's good, chances are you should just play more games to gain more probability to get the win-rate you deserve.
