I use this gun a lot and these are my favorite builds. Adjust to your liking but toughness and QuickDraw are almost mandatory. Silencer works great, and fast mags is nice but not necessary if you're accurate. I usually get 3-4 kills per mag. The only other attachments I recommend are optics if you don't like the irons.
I don't always take cover when I'm being shot at. But when I do, I didn't.
All I can say is avoid Select Fire like the plague, and use the Stock. After that most people would argue Target Finder to be the best universal attachment, unless you don't believe in that particular attachment.
Honestly, since I started using Stock on my AR's (especially the FAL and SMR) I win a good deal more gunfights with them simply due to strafing without feeling like I'm stuck in quicksand. At first I avoided it cuz it felt overresponsive, but it's SUCH a good attachment when compared to some of the more watered down alternatives (post-quad-nerf select fire is a good example).
In this game I think you either have to run Ghost or have an FHJ to shoot down UAV's, so that dictates all my classes. Maybe I suck, but I don't like playing when all my enemies know where I am. Bit of a disadvantage, that.