Always placing your crosshair at head-level while moving around the map is the best way to improve as a beginner. Sometimes you only get one or two bullets out of your gun before the duel against an enemy is over.
It’s tempting to drop your crosshair placement while running between locations or when swinging to an area that you think is clear. But if two players catch each other by surprise, the player with their crosshair already placed at head level will likely win the duel. Make it a habit to always have your crosshair ready to make a headshot, and never let it roam around the screen aimlessly, even when you think you aren’t in a battle.