Use the correct size screwdriver or bit and press down firmly
Tap the screwdriver into the screw head with a hammer for better grip
Place a wide rubber band between the bit and the screw head
Try a manual impact driver
Use locking pliers if part of the screw head is exposed
Cut a new slot in the head with a rotary tool or hacksaw
Apply penetrating oil and wait before trying again
Use a screw extractor kit
Drill a small pilot hole and use a left-hand drill bit
Drill out the screw completely if needed
Replace the screw after removal