Open and shut the door slowly to locate specific spots where the door sticks or drags. Identify any scuff marks on the door frame that reveal where the door drags across the frame.
Wrap a sheet of 80-grit sandpaper around a wood block. Partially open the door and sand the door edges where the door sticks to the frame.
Shut the door and open it back up to verify it doesn't stick anymore. Continue sanding any sticking spots on the door edge until it opens and shuts freely.
Use the screwdriver to remove the screws from the door hinges, starting with the bottom hinge and working up to the middle and then the top hinge. Take off the hinges only if the sticky location is in a spot you can't reach with the sandpaper with the door in place--for example, the door bottom.
Remove the door and position it so the edge that needs sanding is facing up or otherwise gives you access to it. Enlist a helper to hold the door steady while you sand the door edge with the sandpaper.
Reinstall the door, tightening the screws into the hinges with a screwdriver.