Use the correct size screwdriver and press down firmly
Tap the screwdriver into the screw head with a hammer
Try a rubber band between the screwdriver and the screw
Use locking pliers if any part of the screw head is exposed
Apply penetrating oil and wait a few minutes
Use a manual impact driver
Cut a new slot in the head with a rotary tool or hacksaw
Use a screw extractor kit
Drill a small pilot hole and use a left-hand drill bit
Drill the screw head off if necessary
Remove the part holding the screw to get better access
Apply heat if the screw is stuck with thread locker
Replace the screw after removal