Use the correct screwdriver bit and apply firm downward pressure
Tap the screwdriver into the screw head with a hammer
Try a rubber band between the bit and the screw head
Use locking pliers if any screw head is exposed
Cut a new slot in the screw head with a rotary tool or hacksaw
Use a manual impact driver
Apply penetrating oil and let it sit
Heat the surrounding metal to loosen corrosion
Use a screw extractor kit
Drill a small pilot hole and use a left-hand drill bit
Drill out the screw head if necessary
Replace the screw after removal