Turn off the washing machine, and open the door.
Spray a cloth lightly with mildew remover, and wipe the rubber seal along the door to remove any mold or residue. Lift up the seal and check for any lost small items like socks. Wipe underneath the seal to remove as much residue as possible. If you don't want to use mildew remover, dampen a cloth with hot water and apply two drops of dish detergent and clean the gasket.
Dampen a cloth with warm water, and wring it out. Wipe the rubber gasket to remove the cleaning residue.
Dry the rubber gasket with a clean cloth, and leave the door open to air out the machine.