I'm probably being stupid and everyone knows this, but I'm posting it anyway for people who don't know about it.
I've always had problems aiming down sights as the guns iron sight always obstructed my aiming recticle, and so therefore I ended up just spraying from the hip as the sights on guns such as the plamsa gun really obstructed me at longer ranges when aquiring targets and aiming.
However I noticed fairly recently the option to disable iron sights in settings, and boy has it made a differance. I still get the precise spread pattern and zoom of ADS but without the weapons iron sights getting in the way. I'd reccommend trying it if you are having the same problems as me with aiming.