When a dishwasher is not cleaning well then it's usually because of a clogged drain or filter that traps food debris.
When that filter is clogged the dishwasher will circulate dirty water and not clean water to get the dishes clean then your dishes may just come out dirty or not as clean as they should.
The filter location is usually towards the bottom and usually a plastic cover with holes in it is where the filter is and remove that with your hands or a flat screwdriver is usually how you get to it.
Make sure the dishwasher is clean and the water can circulate properly.
Also be sure to remove large food particles so that the dishwasher does not become clogged.
Dirty dishes can be put into a dishwasher and the dishwasher will do the work of cleaning the dishes.
But if you have large food particles on the dishes then you should clean and scrape those food particles off the dishes before putting the dishes into the dishwasher.
The larger food particles may cause a clog in the dishwasher drain screen.
Also some dishwasher machines have a hard time of removing really hard to remove large food particles.
So remove the larger food particles and then place the dishes into the dishwasher.
If there's no large food particles or hard to remove grime from the dishes then I place them directly into the dishwasher.
But if there is hard to remove grime or large food particles or even small food particles I remove those first so they do not clog the dishwasher drain screen.