Aww anon, I’m sorry you deleted it. :( But I know how those writing related worries can just pile up and get out of control, so I can get where you’re coming from.
I’ve only written one fic in the past that involves oral, and it was from the POV of the guy receiving, so I don’t know exactly how helpful I’ll be here … but I’ll give it a shot.
I tend to stick to canon as much as possible (sometimes to the point of sticking too closely to it, but that’s an entirely separate issue), so if I was writing a sex scene that’s the first place I would go. Do we know the character’s perceptions of sex? Have we seen them engage in sexual activities in the canon? And then, in the case of a shipping fic, have we seen them be (sexually) intimate with (insert character of choice)?
From there we can choose where to take things. You can use the building blocks of what the canon provides (assuming they exist) and explore further, or you can use them to take things in an entirely different direction. Sometimes the character is a blank slate and you can do practically anything you want.
… The basic rule I try to follow whenever I write fic is that the content can be as out there as you like, so long as it’s consistent within the context of the story you’re telling. So, an example (generic and most likely inaccurate, but as I don’t know what fandom you’re writing for I’m just making something up): character A is giving character B oral, A hasn’t done it before, so when the moment comes (no pun intended), A spits because they’re uncomfortable and don’t know any different. Or, if you wanted to do it a different way, A swallows, but they don’t know how they feel about it afterward. Whatever the character ends up doing, their inexperience is the centre of it all, and provides the basis for their actions and reactions. (Of course there are a multitude of different options at your disposal - this is just a very basic example.)
I don’t know if any of that was useful, but the point I’m trying to make is: you can write it any way you want, essentially. If you want to stick to canon, do so. If there’s nothing in the canon to help you, do your own thing. Everyone will interpret a character in their own way, so regardless of whether you choose to have the character do what you’d do, or try to imagine what the character themselves would do, at the end of the day you won’t be “wrong”. It’s just your interpretation of this certain character in this certain scenario you’ve devised. So long as there’s some internal consistency behind their actions (and in their world) you can have them do virtually anything.
… That was far more long-winded than I intended. Of course they’re all suggestions - you don’t have to pay them any mind if they don’t suit you.
I don’t know if any of this helps. I hope some of it does, at least. Feel free to message me again if you want to talk more.