I’ve written a reasonable amount of erotica, some of which has been guro-themed, and been told it’s good. So I’ll weigh in with my personal advice, but do bear in mind that this is in no way ‘official’. I don’t have any actual qualifications lol, all I know is what works for me. I’ll also avoid repeating the basic stuff others have said about grammar, tense, etc, but that is all vitally important to consider.

Writing guro is very similar to writing regular erotica. The specific acts being described are different, but the overall tone is still meant to be arousing. I find that in order to accomplish that, firstly, word choice is very important. You want your words to be very blunt, to the point where they shock the reader and give them that taboo thrill they’re looking for. You’d be surprised how many ‘adult’ stories still dance around the hardcore subjects with flowery language. People aren’t used to reading about others being intimate in explicit detail, so when they see a story like that, it’s exciting because it’s different. Also bear in mind that I don’t mean be vulgar (using ‘fuck’ and ‘cunt’ all over the place is, in my opinion, not very arousing; like when you get these women just screaming ‘fuck me’ over and over again in porn and it feels like it’s trying too hard). But be explicit and try to use evocative, visceral words. This is probably easier to do in guro than in regular erotica because you gain access to the whole lexicon of violent language, not just sexual language.

Second, another very important thing is to have a strong description of your characters’ internal feelings and monologues. This may be more personal preference, but I find that lots of erotica (both guro and not) falls into the trap of reading like a drawn-out grocery list of sexual or violent acts. It describes what one character does to another, but it ends up feeling flat and boring because we have no connection or interest in what’s happening. You don’t need a detailed plot or backstory, or even very 3-dimensional characters, but you do need an insight into what is going through their heads during the act. I think a story that only features a relatively brief sexual encounter, but delves into the emotions of the characters at each point, reads far better than a story that just goes on and on with who did what when. Again, guro works well for this because there are so many visceral emotions to draw on.

Thirdly, and closely related to the last point, consider who your pov character is. I think guro works well written in the 1st person, as that really lets you get into the mind of a character, but you can do 3rd person if you want to give insight into how both parties are feeling. Either way though, whoever the current pov character is, tailor the language and style to their role within the scene:

For example, consider a standard guro scene of a man violently raping and butchering a woman. If told from the woman’s point of view, it’s vital that you use emotive description to convey how truly awful it is for her. We should feel her pain. Describe in depth her fear, her feelings of helplessness, her shock and disbelief at what is being done to her, and the agony and shame she feels as her body is violated. Address the moment where she realises she is going to die, or at least, be left permanently crippled and deformed. If each wound being dealt to her is accompanied by thoughts like that, it makes the whole thing more impactful.

From the man’s point of view though, it’s the opposite. He is the aggressor, and the one enjoying himself. You should describe his glee, and the moments of thought and inspiration he has before each act. Is he going to cut her clit off with a knife? Why did he choose to do that and not something else? When describing the woman as seen though his eyes, use objectifying nouns and adjectives; as if you were describing a piece of meat or any other inanimate object.

That’s just one example, but hopefully you can see what I mean about fitting the language to the character and the scene.

Third, have some fun lol. Don’t stress about getting everything exactly perfect, especially not first time though. Write what you want to write and let your creativity flow, even if you know at the time you will want to go back and touch up sections later. It’s much easier to adjust something that’s already there but imperfect than it is to write something perfect from scratch.