I have been playing this for a while and I am climbing the league very fast. Most of the time I get top and MVP at the end of the game.

I try my best to aim for headshots, as it does the most damage to enemy. Sometimes they don't even have time to react to shoot you if you were to put all your bullets at once in their head.

The way to do so is to try and keep your crosshair at head area since everyone have the same height. Stay at that height most of the time. The rest is just adjusting left and right to shoot them. If you are at a bit higher ground, chance of getting headshot are higher. Not those area that are super high it would be harder to shoot.

Mouse Sensitivity
That is also a key thing to help you get a good aim, I have it by default and I am doing fine. Since characters doesn't move fast. Aiming for head shouldn't be that hard.