1) The extremely ordinary girl who is average, plain, and bland in appearance, personality, and general character development and who constantly talks about how boring she is and how there’s nothing special about her. This character is boring. This character is flat and static. The plot throws her around and everyone else figures things out for her. What she does do is make one or two very asinine decisions. Authors often use that as an opportunity to let a male love interest step in and fix everything for her. She then moves on from the mistake without having learned or without having changed from the experience.
Your characters, especially your protagonists and main characters, deserve so much more than that.
I should say that characters who genuinely believe there is nothing special about them do not fall into this. The characters who don’t genuinely believe it are the ones who mention it in a nonchalant way when they’re confused as to why someone would like them romantically and who then never mention it again. This belief is not shown in their dialogue, their emotions, or their behavior. They never express their concerns and no one else notices that they have low self esteem.
2) Female characters who are tokens. They’re introduced as the Strong Female Character, or what authors think a strong female character is, and do nothing but nag to show that women are always right and men are always wrong. They contribute nothing to the plot, are not well written, and rarely have relationships with other female characters.
3) The evil ex girlfriend needs to go or at least get an upgrade. She often shows up with the first character I described. She’s the ex girlfriend of the hot guy who is in love with the super average girl and she’s often the opposite of the protagonist. The protagonist is kind, gentle, innocent, and pure. The evil ex girlfriend is rude, dresses provocatively, hates the protagonist, and is an antagonist. This author gives all traits they consider immoral to this character and they’re used as a tool for preaching.
There are a lot of things wrong with this character, including sexism, blatant “white and black” morality, the “virgin vs whore” symbolism, and general craft failure. I think the only well written version of this character I’ve seen is Regina George (prior to Janis’s plans to mess with her).
Another version of this character is the “crazy ex” who stalks the male love interest and who is often referred to as being insane or mentally ill. These characters are less common in the YA age group though.
4) Female characters who are only love interests. These characters can be taken out of the story without losing anything important to the plot or characterization. This is craft failure.
5) We need to stop “fridging” female characters. This is when a female character is killed off by the bad guys for the purpose of angering the male protagonist. The death most often happens in the beginning of the story or shortly before the story begins. This trope is used way too often.
6) Female characters who are used to show that femininity or being attractive is inherently bad and that it makes other characters like that bad people. These characters often complain about other female characters and prefer to hang with the boys because they’re “not complicated” or something.
7) This next character isn’t one that we need to get rid of, but one that needs to allow others to take the role of the protagonist. I see so many times in fiction, particularly in speculative fiction, that female protagonists need some unique skill or ability to be the protagonist. Male characters get to be the unlikely hero who comes from humble beginnings just as much as they get to be someone with a unique ability. Female characters don’t get that chance too often.