If you are lucky, a piece of the broken key may protrude from the lock. In this case, you can try using the tapered beak clamp to remove the key. If you don’t have the tapered beak clamp, use a pair of scissors instead.
But just in case you cannot see the broken key protruding out, don’t be upset. The lubrication of the keyhole cylinder & its alignment will help you pull out the key. Use pliers, tweezers, or scissors to help you get this task done.