Use the correct screwdriver or bit size
Apply firm downward pressure while turning
Try a rubber band between the screw and driver
Use a larger flathead if the screw head allows it
Tap a slightly larger bit into the stripped head
Use locking pliers if the screw head is exposed
Cut a new slot in the head with a rotary tool
Apply penetrating oil and wait
Use a screw extractor
Drill a small pilot hole and remove the screw with an extractor bit
Drill out the screw head if necessary
Replace the screw with a new one
Prevent future stripping by using the proper bit and torque