Spray a small amount of lubricant into the lock
Align the broken key fragment with the keyway if visible
Use needle-nose pliers to grip and pull out any protruding piece
Use tweezers if the fragment is shallow and accessible
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 loosen the fragment
Avoid pushing the fragment deeper into the lock
If the fragment will not move, call a locksmith
Replace the lock if removal is not possible or the mechanism is damaged