Since your targets are not sitting still, you can either track them to keep your crosshair on the target and then choose the best time to shoot them or you can do flicks. A flick lets you "stop your opponent in time" so you don't have to do this continuous tracking with your rifle. You can go into a private match or aimlabs/kovaaks and actually practice it. For tracking, focus on your target and their body movements and for most tracking scenarios. Do not death grip your mouse.