Very effective at singling out stray kills. Only attempt when you have a more powerful weapon than your opponent. Refer below pic for example. In each case, they are stuck with no choice but to die. Let’s say your opponent is camped somewhere and they must move. They have an exit that you’re aimed at. Camping outside this exit will make them nervous and they might choose to rush, which works to your advantage. If not, no one’s stopping you from throwing grenades/gas at them. The idea is to force them to give up the kill. If you’ve played a fair share of online games, you’d have been in situations where you know you will die. A pro player acts out of his instincts and manages to either save himself, or to kill along with die. Do not give this choice to your opponents.
Reduce your zoom and wait patiently. Stay still on their only exit, and fire as soon as they show up. You can only get good at this by playing with other pros.