When you are writing a story, you want to create unique characters for it, not cookie cutter stereotyped characters.
Don’t create a dark shadowy figure that lurks in the shadows of an alley. Create a real character that watches your hero from the gloomy depths of the alleyway.
Rather than a busty blond or nondescript brunette taking your hero’s order in the cafe, maybe their order is taken by a young man that has traces of grease under his fingernails from his second job as a mechanic.
A danger zone is in too much detail, however, which can be just as bad as a character that is too classic a stereotype. Yes it might be stereotyping to have a meek bespeckled librarian, but just as dangerous is to toss out all of the traits of your stereotypical librarian. There should be aspects of the character that, while not what one might expect from the role, are also universally expected.
For example, a librarian might be different in their body builder physique, but they likely still love books or they would not have become a librarian.
A good exercise is to take a sheet of paper and write the kind of character you are creating at the top. Then draw a line down the middle. On the left write everything you think of when you think of that particular type of person, including and especially stereotypes for them. Then on the right side of the paper write all of the things you need for the character in your story. From these two lists you can create a character that has the traits of both what you need and what you expect, and from that you can create a non-stereotypical character or your story.