A common thing you'll see on here and other games, is being called a hacker is considered the ultimate compliment. Why? Well if this stuff helps out, and you get called one, you'll know the feel bro.
1. Understanding spread
If you've played first person shooter before, you might have heard on the concept of spread. Simply put, spread is a dynamic value that determines the angle at which the bullets exit the gun. Keep in mind this IS a hit scan game, so this is pretty crucial to know cause it determines how the gun will behave.
First of all, when you fire the gun, it will bloom, when you stop firing, the bloom will reset to the initial starting accuracy. So, STOP SPRAYING, fire in controlled taps at the enemy's head, preferably just above and or to the left of their head. Reason why is because hit models typically move ahead of the rendered models, it's one of those weird things with multiplayer, get used to it.
So, to refresh, fire in bursts or tap out your shots, aim slightly to the left of the forehead, and you'll do fine.
2. Strafing is key
Regardless of how you aim, one helpful tip is to learn how to strafe properly while keeping your cross hair lined up vertically with the enemy's head. You might have heard the terminology "head level". this is basically the same, if you drew a line from left to right, you crosshair would line up with the enemy's head perfectly, meaning all you have to do is mash your a and d (or s and f) keys a so you can stay on the move while consecutively squeezing out shots. Done right you'll land headshots constantly while being difficult to hit.
It also helps to mirror your enemy's strafe, most people are right handed, so they'll commonly go to the left on your screen, so, stay ahead of them slightly and you'll nail them.