How to be better in video games, from a pro player.

So, let's start with a bit explaining who I am:
I was an average veteran League of Legends player (don't spear me). Esports was getting big, and I decided that esports would be something I'd love doing. I dropped out of a Business College (but enrolled in an online college, which I continued to do at nights as a backup plan) and started practicing. I shortly reached top 500, and went on to top 50 on the Europe West server. I got asked to join a team, and started scrimming 8 hours a day against "A" tier (and sometimes "S" tier professional teams (Na'Vi, Gambit, Pain Gaming and countless others). League of Legends "A" scene was in a bad shape, with no communication from Riot and due to the grip they had in organizing tournaments, and countless bad decisions they made I started quietly checking out other games. I went over all of the MOBA's in development, and the current popular ones. Dota just seemed fitting, so I decided to play Dota for a month on my free time and see how it is. I fell in love instantly. (Especially since in League, you have a pre-defined way of making your impact, and it's about making less mistakes in that specific way of making your impact. In Dota, you have free hands to make your impact, you don't have a predefined, set path but you get to choose your own path and you have almost free hands to excel. )
Alright, so now you have a general idea about the writer of this small piece. Let's talk about a thing I see many people repeating, and which is clearly holding them back. First of all, you have to understand the difference with playing and practicing. You play for fun, and you practice to improve. That's also why sometimes more competitive players get frustrated when playing with friends, who are playing for fun when you're playing to improve and win.
I see many player associating defeat, committing mistakes or dying with a negative feeling. THIS IS A HUGE MISTAKE! Losing, dying and making mistakes highlights them. As long as you are using your head, a loss streak can be way more valuable than a win streak. You need to go over each game, preferably after (if not after you should watch a replay, or at least skip through it) and think: What could I have done to win this? What could I have done to not die there? What could I have done to get that kill there?
Once you highlight your mistakes, it's much easier to focus on fixing them. Seems simple huh? This definitely should be your mindset if you want to climb the ladder.
TL;DR: Losing, dying and making mistakes = good. Highlight and figure out your mistakes and focus on never repeating them again. That's how you better yourself as a player.

Also, practicing game mechanics, learning team compositions/character counters and the metagame is very important. With that knowledge and skill, you'll be able to predict the enemy team's actions and prepare for them. In every battle, in game and out of game, knowing is half the battle. It comes down to positioning, skill, and tactics when the encounter starts, and you always want to start a fight with the advantage and through simple statistics, avoid fighting on equal ground.