Apply a small amount of lubricant to the lock
Leave the key fragment in a straight position if possible
Use needle-nose pliers to grip any exposed part of the broken key
Use tweezers if the fragment is slightly visible
Insert a broken key extractor tool beside the fragment and pull it out
Use a thin jigsaw blade or hacksaw blade with the teeth facing outward to hook the key fragment
Gently wiggle the fragment while pulling it out
Tap the lock lightly to help shift the fragment
Avoid forcing the fragment deeper into the lock
If the fragment is not accessible, remove the lock cylinder if possible
Call a locksmith if the fragment cannot be removed safely