There's nothing, really, that we need to remember when writing for teens. Absolutely anything goes.
Ambiguous endings, possibly. As in, avoid them. I recently finished reading an adult novel which ended that way, and forgave it (in spite of my own frustration) because the author was making subtle points about fiction, war and humanity. Having said that, I'd be similarly forgiving with a YA novel, if it were well-written.
But, yeah. I probably would think hard before writing an ambiguous ending to a YA novel.
I have one main suggestion as I was new to YA reading because it didn't exist when I was a teen. (which could be how I ended up reading Lolita at 13). I'd written from adults view points and children but never a teen. I didn't identify with teens when I was one, I was very...unusual.
But I read several a few years back in the Fantasy/Dystopian Genre and they ALL included a romance. Not a problem. But it was sixteen year old girl's falling in love, deeply, madly and for-ever with a handsome boy. Do teens have crushes? Yes. Does it feel like the real thing? Yes. Do you see yourself marrying them? I think most girls would like to think that. But 4 books later in their twenties they are still together. Now how many girls or boys can say I got together with someone at 16-18 and we're still together now. You go through a big change in your late teens and twenties. Your tastes and interests change - mine did a lot. I know some people stay together like that but I don't know any of my friends that are still with their first crush twelve years down the line. So write romance realistically.