Stay calm and avoid forcing the lock
Leave the lock in the open position if possible
Use needle-nose pliers to grip any exposed key fragment
Use tweezers if the fragment is small and accessible
Apply a small amount of lubricant to the keyway
Insert a broken-key extractor tool and hook the fragment out
Use a thin jigsaw blade or hacksaw blade with the teeth facing outward to catch the fragment
Tap the lock gently to help the fragment shift outward
If the fragment is flush, use a strong magnet if the key is magnetic
If the fragment will not move, remove the lock cylinder if possible
Take the lock to a locksmith if extraction fails
Replace the key after removal to prevent recurrence