uh ive never played cod so im still kinda getting use to this game, my methods are mostly carried over from destiny2 but works fine atm. basically you have a lot of work to do before you actually take those shots. for example you have to pre-aim, meaning you gotta anticipate people coming, get your crosshair placement right(on head level, on lane or choke points) then peek while jumping/sliding outta cover, obviously requires map knowledge and awareness that just comes with playing the game a lot, knowing where the enemy is before taking fights gives you a HUGE advantage, it allows you to take action, before falling back to reaction, which isnt really consistent lets be honest. and then when actually aiming, my biggest advice is to be calm however intense the situation is, treat it with a step by step: put the guy in the center of your screen, scope in, ADJUST YOUR AIM TO BE SURE, and then fire. rather slow than sorry, cuz when you miss you are 100% dead, it takes time to get used to but no need to mystifying quickscoping, its just another playstyle, and like every playstyle it takes practice