I have been adding 1 tablespoon of washing soda to my dishwasher detergent when I put it in my dishwasher. I use the liquid detergent and by adding the washing soda it almost doubles how many washes that I can get out of a bottle. About once a week I will run a load with no washing soda and use only detergent. Otherwise sometimes my dishes will get a little filmy.
Also when filling the rinse aide in my dishwasher every other time I put vinegar instead of my regular jet dry. I found that using vinegar always eventually ended up with a film on my dishes. but if I rotate it with Jet Dry it does rather well and saves me money.