To ensure that your dishes are sparkling clean I recommend that once every couple of months (or more frequently if necessary) you do a quick cleaning.
1. Remove visible debris - Pull out any loose debris on the bottom of the dishwasher. Some units have a screen area that will collect these larger pieces of food, etc.
2. Inspect the spray bars - Insure that the holes on the spray bars are free of debris and hard water deposits. If necessary, take a small paring knife to scrape any mineral deposits away from the holes to insure that the water sprays properly and fully.
3. Wipe down the interior - Using a sponge or soft rag and some hot soapy water, wipe down the interior of the dishwasher. Pay special attention to the area where the door seals. Wipe down the seals well and don't forget to wipe down the interior of the door itself.
4. Run a disinfect/cleaning cycle with an empty dishwasher - Place a packet of unsweetened Kool-Aid Lemonade concentrate into the soap dispenser and run your dishwasher on the hottest setting available. The citric acid from the lemonade helps remove hard water deposits and grime. The super hot water further disinfects the interior of the unit by killing any bacteria that may be found. Make sure the unit is empty as the citric acid could etch your glass and stoneware. Double advantage - your dishwasher smells lemon-fresh!
Don't assume that something that is used to "clean" is, in and of itself "clean". Neglecting to care for your appliances both inside and out can result in diminished performance.
Assignment: Next time your dishwasher is empty, give it a quick once over. Run a cycle using a packet of lemonade. If you don't have lemonade, try putting a cup of vinegar on the bottom of your dishwasher and run a cycle.