Locate the stud with a stud finder
Mark the screw location with a pencil
Choose the correct screw type and length
Drill a pilot hole if needed
Hold the item in place
Drive the screw into the drywall or stud with a screwdriver or drill
Stop when the screw is snug and flush
Avoid overtightening
Use drywall anchors if there is no stud
Test the screw for stability