Only run the washing machine when you have a full load. Half load settings on washing machines often use more than half the electricity and water of a full load. Choose a model with a high energy efficiency rating for your next washing machine. Water efficiency is assessed as well as electricity use.
When choosing a new washing machine, assess its capacity. A couple or single person are likely to want to run smaller loads than a family - so choosing a smaller capacity machine, will mean waiting less time for a full load to build up!