I tend to write the medical mechanics of creating hybrids. E. g. people in a lab, messing around with gametes, chemicals, etc., trying to get chromosomes to line up. And sometimes they don't. For E2 (ENT) stories, I write Ikaarans and humans as being interbred via this kind of intervention but there are some extra genes and those are mainly shunted off to molar shape. Tucker and T'Pol have children via petri dish.
I do write one guy who's Klingon-Xindi sloth (arboreal) and human, but he's way into the future. The arboreal part makes him kind of paranoid as that species were prey animals for other Xindi sentient species, and powerful as he's got Klingon going on. The human part makes him a bit slighter so he's got a Napoleonic complex. But he is the only three species character I've got, and the human part is really only in there to make him smaller than your standard Klingon. He has issues and is having an affair. When his mistress starts blackmailing him (spoiler alert), he strangles her.
But yeah, most hybrids, there have to be reasons for this. And species aren't a monolith because we sure as hell aren't. Klingons can be cake bakers, and ballerinas, and marathon runners. Tellarites can be models, and carpenters, and rodeo riders.
Conflict is key in stories, particularly those that are over, say, 500 - 1000 words. There have to be reasons why we are peeking into this particular day.
Oh, another thing - POV. First person, third person limited, third person omniscient? Google these terms. If the story starts out as being in, I dunno, Janeway's head, then she doesn't know what Tuvok is thinking. She can make educated guesses but she does not really know.