In the 'Settings' section you can adjust your 'look sensitivity' (sometimes known as 'aim sensitivity'), which affects the speed at which you can adjust where you're looking. The higher you set it, the faster you can look about and move your aim to a new target, which is good of course. But it can also make small aiming adjustments trickier, causing you to over-rotate. You need to strike the right balance for you.
Players who do a lot of gung-ho close-up fighting may prefer relatively high sensitivities so they can swivel around quickly when dealing with multiple enemies close up. Players who prefer to fight from distance will have less frequent need for such extreme swivelling, and may prefer lower sensitivities to make smaller aiming adjustments as easy as possible. Of course, the right setting also depends on your manual dexterity. The better you are in that respect, the higher the sensitivity you should be able to cope with.
To maximize your combat effectiveness, I suggest raising your look sensitivity as high as you can, subject to still finding small aiming adjustments easy enough. Here's how you might go about this. Starting off with whatever you're currently comfortable with, try raising it a step and see if you can get used to that. If it doesn't work out, go back; but if you think it's an improvement, try another step, and so on. The default sensitivity is 3 but I suspect that most experienced players will use something higher. I use sensitivity 5 which I find ideal for all the medium to long range pistol work I enjoy, yet also fine for when I mix it up close.