First things first I have to say everything I say YOU have to do in order.

get close to your monitor
walk somewhere you can see heads
sit
open your eyes wide as possible
look left and right until you see a color change
(optional) click the head
scope in and hold your breath irl and ingame
aim in front of the person calculate the meter and bullet speed and his speed and your thinking speed at the same time you are going the think you are going to think where you are aiming and calculating the ♥♥♥♥
click mouse1 and there you go you missed.
(optional) click the head again.
now go watch some youtube guides to get better
once you are better ingame come back and
(optional) click the head.
if not skill issue Im trying my best to help and you are not learning it.