Your character wants something, but if they don't get it, what happens? In a contemporary YA novel, usually the answer is, "Nothing." Like seriously, they're teens--what goal could they have that would entail major consequences? Sure, they might want to get into a good college (as in my novel) or get with that guy/girl or become captain of the debate team, but if those things don't happen then so what? Disappointment is a part of life.
This isn't just a contemporary YA problem. I think all novels, to some extent, suffer from the difficulty of creating high stakes while remaining character-driven. The problem is that if your character wants something, then obviously they don't already have it, and if they don't have it, then that means it's possible to live without it.
Conversely, the more plot-driven your book is, the easier it is to create high stakes. If your book is about a masked gunman who enters the school and starts shooting, then your stakes are high, but you also don't have much for your character to do. At that point, your character could be anyone: they're just a human who needs to stay alive for the next few hours.
So how to balance the two: the need for high stakes and the need for characters whose choices actually matter? The solution, in many books, is, as I mentioned earlier, to have two plots. One of the plots, the smaller-stakes one, is driven by the character's desire: in that plot, they're acting first and setting the agenda. The other plot, the higher stakes one, is driven by their antagonist: in that plot, your character is primarily reacting to what someone else is doing. The first plot predominates in the first half of the book, and the second plot predominates in the second half.
For instance, take The Fault In Our Stars. It's a book about kids who are dying of cancer. The stakes are sky high. But the problem is: a) there's nothing for them to do, since an individual can't fight cancer; and b) there's nothing unique or personal about it. So you need to layer a plot on top of it. In this case, there's a love story. That's a plot where the characters have some agency, but there'd normally be no stakes (who cares if two teens get together). But by using the cancer plot as a constraint on the love plot, you have a story. The two plots are very complementary, too, since the love plot is life-affirming, while the cancer plot is life-denying. In the first half of the book, the kids choose to love, while in the second half...well...there are complications.
Or take The Spectacular Now. In the beginning of the book, the protagonist wants to get his ex-girlfriend back. Again, a concrete objective, driven by real desire, but low stakes. However, there's an underlying plot concerning his alcoholism and his fecklessness. If the book was only about his alcoholism and fecklessness, it wouldn't work, because there'd be nothing for him to do: How can you try not to drink? How can you try not to screw up?
But because the two plots are layered together, the stakes build. The second plot serves as a way of complicating the first plot, and now you see the choice the novel offers up: either he'll find love, or his life will fall apart.
This is something that works best for contemporary and less plot-driven books, because in this structure, the bottom plot, the high-stakes plot, isn't as emphasized as it would be in an action-oriented novel or in a mystery. I still haven't quite cracked the problem of structure in those books. For the life of me, I find it very difficult to understand why it's so compelling to see a person solve crime after crime. I know that it is compelling, because I've read Agatha Christie, and I've watched Law And Order, but I don't know quite how the compulsion operates.