Now, I'm certainly not someone to go to if your genre is horror. I don't know how to write a horror book, nor am I particularly into reading horror, or even watching horror movies. Not because I'm too scared. Quite the opposite, actually. I can't get scared when I'm expecting you to try and scare me.
It's a weird genre quirk of mine. Same reason I can't get into romance novels. I can't fall in love with the relationship between two characters when you're trying to make me. I always fall for a pair of side characters, because it feels like the author didn't try to hard to make them adorable. Some things have to happen naturally or they just don't work.
Now it's easy for me to sit here and say "try to be unexpected!" if you write in either horror or romance, but I honestly don't know how to guide you in doing so. So, I'm sorry for that. It's only because I straight up don't know how to do what you do. Like I said, this is a quick of mine, so don't listen to me, listen to your audience.
This post is really for others who write outside those genres. You've got a whole new opportunity to readers by surprise, by dropping in unexpected scenes. When I see a horror scene in a place I don't expect, it's way more terrifying than an entire horror movie, because I didn't have time to prepare myself.
For a weird example, I'm a huge fan of the show "Legends of Tomorrow." I expect time travel, fun, and chaos from this delightful mess of a show, and it always delivers. Then I watched the episode "Night of the Hawk," and it scared the crap outta me! I was not ready for that horror-movie level stuff! But if that whole concept was it's own horror movie... Nope. I wouldn't find it scary.
People I've spoken to in person who have read "The Mansion's Twins" usually comment on a particular scene: the room that lulls it's victims to sleep, and then kills them. They'll say things like, "That was SOOOO creepy!" And I'm like, "Really? Awesome, I didn't know I could do that!" But what made that scene (I think) was the horror-movie nature of it, put inside a YA fantasy novel.
The only risk in dabbling in other genres is that it can be jarring for readers if you step too far outside. Don't switch genres mid-book, pull elements and inspiration while staying true to your world.
Get inspired out there, and have a Happy Halloween!