Habits
Crosshair at head height, always
In one line: Keep your crosshair at head height even while walking or turning.
Why
Most duels are decided by the first shot. If your crosshair is already where the head will appear, you only have to click; if it is on the floor, you first have to move it, and the enemy shoots first.
How to train it
For one game watch only this: every time you round a corner, check where your crosshair is. The chapter on crosshair placement explains how to train it in the range.