Not washing dishes properly - clean fil...

Would help if you give make and model number.

However it usually involves taking out the bottom assembly with the spray arm, strainer etc. and cleaning it out manually.

You also could try running it empty with a couple of cups of white vinegar - if it is grease that should clean it out. If it improves but not completely repeat it.

Also if you have a drying aid dispenser make sure it is not empty.