Here's what I notice when I read a lot of YA fiction in a short window: the patterns stop being invisible.
The "chosen one" trope gets blamed for a lot of bad YA fiction, but the problem isn't the trope. Katniss Everdeen is a chosen one who volunteers in place of her sister, and the rest of the series is about what that choice costs her psychologically. Harry Potter is a chosen one by prophecy, but Rowling spends seven books making him earn it anyway. The trope fails when it replaces character development, when being special is the whole personality. Done well, being chosen is the inciting incident, not the identity.
Love triangles in YA are structurally closer to a chess fork than a romance. The protagonist is the piece under threat, and the two love interests represent diverging futures. The Peeta-or-Gale question in the Hunger Games is about which version of Katniss can survive what she's been through, not about which boy she likes more.
Adults in YA fiction are almost always unreliable, absent, or wrong. This bothers some readers, but I think it's one of the most honest conventions in the genre. Teenagers do experience adults as inconsistent authorities. S.E. Hinton wrote The Outsiders at sixteen and barely included a functioning adult in the entire book, and that silence said more about her characters' world than any exposition could have.
The special power or ability in YA is almost never really about the power. Telekinesis is anger you can't control. Mind-reading is the terror of knowing what people actually think of you. I'm not sure every YA author is doing this consciously, but the best ones understand that the fantastical ability is a metaphor for something the protagonist can't yet articulate about themselves.
First-person present tense dominates YA fiction tropes and conventions, and there's a cost that doesn't get discussed enough. You gain immediacy and intimacy, but you lose the reflective distance that lets a narrator be wise about their own past. John Green's The Fault in Our Stars uses first person past tense, and the slight distance is what makes Hazel's voice feel considered rather than reactive. When everyone defaults to present tense, the books start sounding like they're narrating a livestream.
Patrick Ness once said he tries "to write for the teenager that I was/still am" and wanted "books that took me seriously, that took my challenges and opinions as real." That's the tension at the center of writing for this audience: you're writing for someone who is both less experienced than you and completely unwilling to be condescended to.
The school-as-society thing. Hogwarts has a rigid class system, literally sorted into houses. The districts in the Hunger Games are just school cliques scaled to something far worse. Sherman Alexie's The Absolutely True Diary of a Part-Time Indian puts this most bluntly, with Junior navigating two schools that function as two entirely separate social economies. YA keeps returning to school settings because school is the first place most people encounter institutional power.
Nearly every YA protagonist is an outsider, and I wonder sometimes if this has become so standard that it's lost its meaning. When every main character is the one who doesn't fit in, fitting in becomes the unusual position. Holden Caulfield's alienation felt radical in 1951. By 2024 it's the default setting.