1. Ensure the machine is not over loaded.
For more information see the Basics of loading the appliance topic.
2. Check the programme cycle. It may be that the dishes are too heavily soiled for the programme selected. Try an longer hotter programme.
For more information see the Running a wash cycle topic.
3. When loaded, check that the spray arms move freely and do not get caught on items being washed.
4. Check for blockages to the spray arms nozzles in particular, dirty spray arm nozzles will reduce water flow during washing.
For more information see the Cleaning the spray arms topic.
5. Halve the dishwasher tablet if the lid is difficult to close. Detergent may not be released properly if the lid is too tight.
6. Alternatively use a detergent with bleaching agents.