ooo this is such a good question anon i have so many...first of all i love au's, give me all the au's especially modern au's! (i know this is a divisive opinion but,,,i just love seeing characters i love in new environments and how they might act/interact with their surroundings - it's a feeling like when you get to go to the market with your crush from work/school or smth. totally mundane but it's elevated somehow by the people inhabiting the space. hope that makes sense lmao)
i tend to write a lot of the tropes i enjoy so coworkers is a big one, uneven power dynamics, misuse of power dynamics. it's so interesting to me how behaviour changes when characters have/think they have the upper hand, and conversely when they lose it. voyeurism tropes is a big one too, being observed knowingly or unknowingly, the observer effect. Characters' behaviour changing by virtue of who might be watching. Especially tasty if who's watching isn't who they think is watching :)
enemies/rivals to lovers is fantastic too! especially if the pair in question is taken out of their normal environment/dynamic by external causes and forced to interact and work together, and in that process learn new things about each other. I'm a sucker for any psychological/thriller/horror/crime elements too...give me all of those. there's probably (definitely) more but this is already a novel haha