How do I stop a door from squeaking permanently?

The most permanent fix is to lubricate the hinge pins with a product that won't dry out or wash away. Remove each hinge pin by tapping it up from the bottom with a screwdriver and hammer, then coat it with petroleum jelly, beeswax, or white lithium grease before reinserting it. Avoid WD-40 as it evaporates quickly and the squeak returns. If lubrication doesn't solve it, the squeak may be caused by loose hinge screws or a misaligned door. Tighten the screws, and if the holes are stripped, fill them with wooden toothpicks and wood glue before re-driving the screws. This addresses the root cause and typically eliminates the squeak for years.