Set the door flat on a work surface. Identify the hinge side of the door; the hinge side is opposite the door handle side.
Measure down from the top of the door 5 inches, on the hinge side, and mark the measurement with a pencil. Place the top hinge here.
Measure up 10 inches from the bottom of the door, and mark it. Place the bottom hinge here. There is always more distance between the bottom of the door and the bottom hinge, than between the top and the top hinge.
Find the center between the top and bottom hinge. Mark the center point on the hinge side of the door with your pencil. This center point will accommodate the center hinge if applicable. Not all doors have three hinges.