There are literary 'awards' for bad sex in fiction. Not for bad fight scenes, or bad dialogue (although that commonly features in explanations of why bad prose is so awful), and not so much for cliched character descriptions (although there perhaps should be one there). Just knowing that is almost enough for me to 'fade to black' whenever my main characters show an interest in each other or in a less central character. Except sex scenes can be integral to the story, and may sometimes be needed to move the plot and character development arcs along.
So what to do? Usually I try to mix what's happening to the characters, with how my character feels about those actions. Pretty much the same as writing any other action sequence really, if only it wasn't for that inner critic that is far more insistent as to whether humans really bend that way than it is when I'm writing about characters fighting, fixing cars, or scaling tall buildings.
I must admit, as a reader I tend to skim sex scenes that are all action and anatomy with little or no inner dialogue. Conversely it's easy to get confused by scenes that are all thoughts and speech with no real explanation of who's doing what to whom. The worst offense, though, and one I try desperately to avoid, is the crime of characters suddenly losing their distinctive voice when they fall into bed (or onto any other suitable surface) with each other.
Over to you. Do you prefer actions or feelings, or an equal balance of both? What good or bad examples can you think of?