Stop.
You suck?
Stop. Playing clever won’t help you; Not when, even though the other player is one shot, you aren’t landing any damage on them.
Anybody above me who said ‘Play clever! Do this! Do that!’ is WRONG. Take it from a person who sucked as well. And now? I’m number 1 on the leaderboards nearly every game. 
Here’s what you do.
Put down the controller. Breath in. Breath out. Ignore the fact your stats are about to sink so much that in the future, when a person who sucks with a negative k/d sees yours and wants a tiny little bit of satisfication, and challenge you to a 1v1, you’ll beat them SO BAD, they’ll cry.
Then pick up the controller. Pick Big Team Battle.
Sit behind cover. Use a DMR. And just aim, and shoot. Start with a 3 sensitivity.
Shoot the crap out of people. Just shoot. Don’t think about shooting;Don’t think about aiming. Just shoot. And then you will find out: What is the best way for YOU to shoot? Is it to dragscope? To move the reticule along with the body? To do small flicks so every time you shoot a bullet the reticule is on the player? You learn it.
Then, once you learn it, you practice. How?
You start moving around behind your cover. Use a DMR. And just aim, and shoot.
Do it. For a long time, do this. And then, one day, you will stop. You will put down the controller. And you will realize, ‘Hey! I can aim now!’ And then, you move up one sensitivity. And you do it all over again. Why? Because as the sensitivity increases, so too does your skill level. Aiming becomes muscle memory; There is no thought involved for me to aim at a head and 5 shot someone. There is only the trigger and the right stick. Want a low sensitivity? Sure! But you will have to move your stick much more. And then you think less.
Think. Are you good enough with aiming? If the answer is, “Hey! I can kill moving targets who aren’t shooting back at me!”
And then, when you do that, THEN what the people above me are saying will be correct. You can start playing clever; Slowly, you adapt to other people hitting you when you shoot back. You learn to stop that from happening with cover. You learn to select yoru targets.