Mirror checks must give you information that changes or confirms your decision; simply moving your eyes toward a mirror is not enough.
You should know what is around and behind the car before signalling, changing direction or changing speed, including blind spots where necessary.
These examples are for understanding and practice; they are not a promise that a particular mistake will always receive a particular grade.
Braking or changing direction before checking the relevant mirror.
Looking in a mirror but then making a manoeuvre that forces another road user to react.