Leave the washing machine door open after use so the drum and gasket can dry, especially if you have a front-loader. A small opening is usually enough, but close the door if it poses a risk to children or pets.
Essential Concepts
Let damp surfaces dry; clean residue that remains. Related posts: [How to Clean a Washing Machine](/how-to-clean-a-washing-machine/) and [How to Remove Washer Odors](/how-to-remove-washer-odors/).