Inspect the hinges, spring closure and weather-stripping, and if any are damaged or showing signs of wear, replace as needed.
Adjust the tension lever on the spring closure. Keep the door closed when adjusting the tension. Make several adjustments and test the door by opening and closing it after each adjustment.
Tighten the screws on the hinges, or if they seem overly tight, loosen them a bit to see if the squeaking noise stops.
Apply a layer of lubricant to each hinge and the door closer's connecting pins. Use any household cooking oil or spray lubricant. Wipe or spray the lubricant evenly along the parts and wipe away any excess with a soft, dry cloth.