I'm sure you've been told to avoid stereotypes in your writing. Stereotypes are bad! Stereotypes are boring! Stereotypes are narrow-minded! Stereotypes are Mary-Sues! (Have you noticed how people stereotype stereotypes?) Regardless of how true any of those statements are, the real reason people say to avoid stereotypes is because generally, stereotypes are an indicator of lazy writing.
If you ask me, there's nothing inherently wrong with stereotypes, not even in your writing. Many stereotypes exist for good reason. You can insert your own stereotype justifications here, because I don't want to be on anyone's blacklist. Stereotypes can show up in literature to satirize, to make a joke, to prove a point, whatever. The problem with stereotypes in writing is that they generally appear unintentionally because the author doesn't care enough to ask, "What ELSE?"
If I ask you to picture a female high school bully, I can pretty much guarantee your mind is off somewhere in the direction of Mean Girls. Mean Girls totally stereotypes the "mean girl" because the whole movie is pretty much a satire of girls like Regina and her posse (after all, "Regina" means "queen"). The image you probably have in your head is tall, skinny and yet curvy at the same time (however that happens), blonde, stylish, relatively stupid, and caked with makeup. I know girls like this and they can be real pains in the rear. But not all "mean girls" are like this.
You decide that your character is a freshman who gets tormented by the junior prom queen for being a geek. But why the junior prom queen? What ELSE could be happening? Maybe your character is a freshman who gets tormented by another really smart and arrogant freshman for being a C-average student.
The point of this essay is to get you to think about what you write. Does the love interest have to have great hair? Does the librarian have to be mean and tightly wound? Does the villain have to have a long neck and a pointy chin? But look beyond physical characteristics here; this applies to everything. Plot, setting, character development. Your main character could live in an orphanage, but what if he's just a middle-class guy with a crazy imagination? He could be really bitter about his parents' divorce, but what if he's happy about it? Why would he be happy about it? Does he ever hate himself for being happy about it?
When asking "what ELSE," you always wind up with more questions than you started with, but that's the point. The point is to think. What would it really be like? How would it really be? Put yourself into the character's shoes. Example: I'm on the tall end of the spectrum, and my best friend is ten inches shorter than me. She complains about being short because people don't take her seriously, and everyone thinks she's like 12 even though she's about to leave for college. Waiters always give her and her siblings kids menus, even though they're all too old for that. On the other hand, I've always wished I could be shorter because I'm taller than almost all my friends. It's awkward to wear heels to formal events. There are pros and cons to both situations, and it's important to think through them.
I'm just throwing out examples to get your brain spinning. The world is full of pros and cons and impossibilities and ironies and anomalies, and it would be a shame to pass all those by for the first idea that pops into your head. You're a writer, and because you're a writer, it's your privilege to examine ALL the possibilities. Don't settle for the obvious explanation.