P.A.S.S.

P= pull the pin
A= aim
S= spray
S= sweep

Lots of people forget to pull the pin when their adrenaline is pumping. Holding the tube at the flames is amusing, but not effective. You have to move back and forth, covering EVERTHING! You need to be on your game because they don't spray for very long either (subjectively speaking).

Fire extinguishers have a lifespan, and most places check them at least once a month.

Practice! The old extinguishers, at a previous job, before they were taken to be recharged they were often put in the hands of someone that had never used one. The time to "try" or "learn" about something new is not in an emergency.

I worked at a foundry, so fires were pretty common. Fire extinguishers work very well at putting out fires and making a HUGE mess at the same time. Given the alternatives I would happily clean up a big mess than rebuild my house. Just my .02cents