The K / D is the total kill / death ratio that each player has in his game statistics, it is determined by the average of the result of each game. This value in all video games also determines the level of the players in the lobby of each game, with which you will go to play against. A higher value will set you against people of a similar value, so automatically lobbies will get harder and harder. For most people it is always very low, so we will see together how to improve it.
First of all you need to understand that increasing it takes patience because the higher that value is, the harder it will be to bring it up. This certainly does not mean that you have to aim for a lot of kills in each game, just limit the deaths and do that couple of kills that will allow you to raise the K / D, trust that it will be enough to do every game calmly to bring it up. .
So at the beginning of each game think carefully before making your move, look around and use the environment to your advantage, always think about how you can cheat the enemy, and after doing a few kills keep your calm. had in the beginning, so you don't panic, avoiding death.
You don't necessarily need to win the game, it would also be enough to finish all games with 3 kills and one death, resulting in an average K / D of 3 for example.
Another good method is to always use the "meta" weapons of that video game, which are the strongest weapons of the corresponding game. You will certainly want to use the best loadouts to be already more advantaged than the others.