I've been paying a lot of attention to writing advice about sex scenes lately and some of it has been quite helpful and eye-opening but in the end so much of it boils down to, "This is just a scene like any other." All the general writing advice still applies: What is the narrative purpose of this scene? Why are these specific characters doing these specific things? How are they feeling and why does that matter? Do you have a good sense of choreography? Of pacing? How effective are your descriptions? What's the tone here? Where's the tension? Are you afraid of your own premise, and if so, can you prevent that from showing in the finished piece? (I'm not going to say that you should never write a premise that you're scared of, because I often do, but are you capable of committing to it regardless?)
Just like sex is a neutral act that people (and sometimes ghosts) can choose to do with their bodies and not something inherently more special and powerful than any other act, sex scenes are a neutral type of writing that's not inherently different from any other scene.
And failing to acknowledge this is a big part of what can make these scenes annoying or ineffective, both for people who want to read them and people who want to avoid them! They're often treated as their own thing, disconnected from the rest of the narrative, and yet also as an inescapable and necessary part of certain genres. They're added to stories where they don't serve any narrative purpose just because that's What's Done, which sucks if you dislike the ubiquity of sex and want stories that focus on other things, and *also* sucks if you want stories where sex is incorporated meaningfully into the narrative and the characterization because they're not doing that either. Treating sex scenes as exceptional isolates them from general discussion of craft, prevents them from feeling integrated into a larger piece, and often makes their inclusion more of an obligation than an active choice, all of which invariably lead to bad writing.
