Leave the door of your machine open after use if you want to help moisture escape and to prevent damp smells.
Keep the soap dispensers clean. Occasionally remove the detergent drawer and clean it using hot water and an old toothbrush.
Check and clean the filter from time to time.
A few times a year, run a maintenance cycle – see the instruction booklet for details.
Only attempt to open the washing machine mid-cycle if your instruction manual specifies you can – some new machines allow you to open to add that stray sock – as on most machines the programme finishes with a cooling cycle designed to reduce both the temperature and the amount of creasing.