Grasp the door, and move it back and forth slowly a few times to determine the origin of the creaking. Tighten any loose screws.
Holding the can upright, spray lubricant onto the screws in the hinge.
Hold the doorknob, and swing the door back and forth a few times to work in the lubricant. If the creaking is still present, use a screwdriver to loosen the screws. Spray a little more lubricant into the holes, and tighten the screws.
Test for creaks by moving the door back and forth again. Repeat the process if the creaking remains. You may need to swing the door several times until the lubricant is worked in thoroughly, and the noise has been eliminated.
Use a rag or paper towels to wipe excess oil from the hinges.