I know when I started playing I used to find it very hard, and a few very simple little tips helped enormously.
I am not trying to be clever here just trying to help. If i state the obvious please delete this and slap me later. In your options menu under view, turn off everything, you want no particals, no blood, no brass. this may help speed up your machine a bit but mainly clears your vision so you can see whilst being shot or granades and airstrikes are going off, it does not effect smoke.
Second one is your cross hairs. A friend told me to just have a little bright dot in the center. mine is green. Since I did this my accuracy has improved no end.
Thats it for now, hopefully others will add something.
Thanks for reading, Cheers.