No Scoping
No scoping is a tough one to get better at, theres alot of chance involved unless you use techniques like a Switch Shot or G-Shot (Try searching these terms on YouTube).
Also, only use as a last resort unless going for a gaming winning kill or something and always try to get their whole body inside your cross hairs.

Try stopping a split second before firing aswell so that your cross hairs shrink slightly to increase your chance of a hit-marker.
Quick Scoping
Try and center their chest (One Shot, One Kill) in the middle of your cross hairs. Also, Sleight Of Hand is a must so you can get the shots of quickly, but even though, don't rush your shots. Make sure that as you fire, you can see your scope crosshairs centered on your target.
Hope this helped a little bit. Try searching on YouTube but even then, it's all down to practising in real matches, though see if you can do 1v1 with one your mates.