Annual dishwasher maintenance consists of 6 tasks:

Clean filter and trap: Inside the dishwasher, the filter and trap are at the bottom where the water drains out. For most models, the filter and trap lift out so that they can be cleaned with a stiff brush.

Clear spray arm holes: Food particle or mineral deposits can clog the hole in the spray arms. Take the spray arms out of the dishwasher, and ream the holes out with a stiff wire. Shake out any loose debris.

Clear the "air trap": Some models have a gap in the discharge plumbing to ensure that water does not backflow into the household water supply. If the unit has an air gap it should be checked and cleaned.

Check and tighten any loose water hose clamps.

Check the door seal gasket for any cracks or leaks.

Check the pre-heating mechanism: If your dishwasher has a pre-heating mechanism for when inlet water is too cold, this should be checked in accordance with your manufacturer's recommendations.