How to win every League of Legends game
Short answer: Reframe what it means to win a League of Legends game.
A huge part of the frustration that comes with playing League of Legends, is losing. Especially losing the games where it feels like the result of the match is entirely out of your control. A truth many players fail to realize is that you are going to lose almost half your games. Even players much better than their elo suggests still end up with about 60-70% winrates as they climb, falling slowly towards 50% as they come to climb and play against players with similar solo queue ability. When people lose, they hate it. Hating losing is not the part that causes problems for many players though, the biggest problem is that people hate losing more than they like winning. This is because of loss aversion. Loss aversion refers to people's tendency to prefer avoiding losses to acquiring equivalent gains. So while your win/loss ratio might sit relatively close to 50%, the losses stick with you harder than the wins. This can tilt you, lead to toxicity, make you play worse, worsen your mood, etc.
How do you overcome this? There is more than one option and different players might find different solutions. My favorite option though is trying to reframe the situation, which is often a solution to overcoming loss aversion. Reframing the situation to focus on yourself and accepting the other factors in the game as things you cannot control. Do not focus on LP, or MMR, or your teammates, or even what tier or division you are in! Go into every game doing your best to focus on yourself. There is literally no game you’ll go through where you don’t make mistakes (bad choice, bad trade, died to ganks that could have been avoided, etc.) So every game there is plenty opportunity for you to learn from your mistakes. Simply playing the game and truly analyzing your plays/mistakes does not leave a lot of room to focus on much else.
If you are participating in a flame war in team chat, all chatting about how bad your jungler is, looking up a teammate to see how bad they are so you have an excuse as to why you lost the game, you are not focusing enough on yourself. If you are hatching Riot conspiracy theories about them trying to keep you down, you are not focusing enough on yourself. If you are blaming luck or teammates regularly for your lack of climbing, you are not focusing enough on yourself. If you are trying to learn more about LP or MMR to blame the system, you are not focusing enough on yourself. NONE OF THOSE THINGS MATTER. YOU CANNOT CONTROL THOSE THINGS. Letting them get to you only hurts your chances of climbing over time, because by focusing on these things that you cannot control, you lose focus on the one thing you CAN control. Yourself.
(I understand venting about such things help relieve the frustration of losing - but if you are playing to improve rather than to win, you will be much less frustrated and over time climb faster and further than you would have been able to otherwise.)
If you play a game relatively well, congratulations! No matter the outcome of the game, you just won. It was a personal victory you as an individual experienced. You still did not play perfectly as perfect play is impossible, so always seek ways to continue improving. Play to improve. Overwolf is a good example of software that lets you watch a recap of your death every time you die. Using a program like that or watching your replays will help you spot your mistakes more easily. Once you recognize them you can focus on avoiding or overcoming those mistakes in the future. There are other methods to practice and improve but I won't go into them here, this article is about overcoming mental obstacles. How you can best improve is an article for another day and maybe even a path you must find on your own.
In short, I see people playing to win/climb and it leads to a lot of frustration. They have issue with Riot or MMR or their teammates. However, those are things you cannot control. Just like you cannot control which dragon will spawn next, you cannot control your LP gain or which teammate/opponent might feed this game. With a more positive attitude that focuses on the individual, you can reframe the situation to make each loss hurt less and make every personal victory feel better. This will improve your attitude, increase the number of games you can play in one sitting, decrease your tilt and most of all, help you improve the quickest.