I was in a match with an M14 and an M60 (a bad setup because it was the starting of the match), and I wanted to aim at a guy at least 90 meters away with the pre- installed scope. I used the scope-in-scope-out trick to give it some damage, but he escaped. From that moment on, I am wondering what the best way could be to hit an enemy with low fire-rate weapons and low-zoom scopes from far away.
Even though it might sound obvious, aim for the head. Aim a bit above the head as when you press the fire button, the aim somehow lowers downwards a bit (at least in my friends and my phone). You will learn aiming better with experience. Besides, the 2x scope obscures the aim, so you pretty much have to guess where you're gonna hit.
Edit: Just to emphasise on the point, games such as Freefire require skill to use whatever what you do along with a bit of luck. You can do crazy things wiht a bit of luck and some skill. I killed an MP-40 guy with M60 with two headshot. You see, top players mostly use default aim precision for the scope-in-scope-out to work so, mostly, the first shot is aimed for the middle of the body. So, you have to be hit badly before you die (that's 200 HP and each SMG does about 20 damage per hit). So using whatever you have to the fullest to win is all that you can do.
Either search for mods that make the gun invisible when scoping, or simply fire from the hip and forget about the 2x scoping. The time you take to scope in is probably not worth much if the target is running fast across your screen. Scoping is mostly if you can take your time to fire. A quick hack to fire from the hip is also to place a small marker on your monitor where the aim's center is.