So double peeking as a concept is quite simple. You peek with your teammate at a lane or a doorway and you shoot enemies together. You create 2v1 situations, 3v2 situations, and try to get the edge on multiple enemies by focusing fire on one target before moving onto the next one. Peeking together allows you to down enemies faster then they can down you and your teammate. It’s a fairly simple thing to talk about but hard to practice and master as it requires an immense amount of trust, coordination, and communication between you and your teammate. Here is a demonstration from my outfit double peeking and triple peeking some doorways and a staircase together to quell enemy players.