Check that the salt or the rinse aid hasn't run out
Make sure that there is salt in the container situated at the bottom of the machine, try topping it up or check the water hardness setting is correct? If you are in a hard water area the setting may need to be increased.
If there are streaks on your dishes check that you have added rinse aid to the dispenser in the door. Try and increase the dosage setting until you are happy with the results.
If you are using 'all in one' tablets and live in a hard water area, try adding some salt into the softener chamber. This will enhance the cleaning results in hard water areas.