Here are some ways you might use "run-of-the-mill" in a sentence:
* "The movie was a run-of-the-mill action flick with nothing new to offer."
* "They live in a run-of-the-mill suburban house."
* "He's a run-of-the-mill employee, nothing special."
Essentially, "run-of-the-mill" signifies that something is just like all the others, lacking any standout qualities.