Pre-aim every angle as you walk. Your crosshair should be at chest height of an enemy who's about to peek you, not at the floor or sky.
Default rule: aim where the enemy's head will be when they appear. For a corner, that's the corner edge at chest height. Adjust as you walk past so it stays consistent.
Most ranked players have crosshair placement at floor level when they walk. They have to flick up + horizontal at the moment of the duel. Pros pre-aim head height all the time so they only flick horizontal.
Practice: walk through a map and consciously aim at every chest-height corner. Build the muscle memory until you don't think about it.