I am not tremendously confident of my ability to write sex anyway. I have alluded to "hydraulic details" before. I guess you need some of that, and the human brain is wired so that a little tugging on the physical basis is thrilling. But the emotions have always seemed more interesting. And my writing tends toward the Hemingwayesque simple declarative sentences enough that I have nightmares about the physical stuff reading like a clinical narrative. "And then Patient X inserted tab A into slot B and moved at a regular rhythm for 3 minutes 15 seconds."
The thing to do is probably to analyze the fiction I've read that I feel is successfully erotic to figure out why it's so. Expect a tedious entry here sometime in the next couple of days that utterly ruins your ability to enjoy some story by dissecting it and leaving its guts out on the floor.
This blathering is in relation to the piercing kink story, which I said had turned into a weird psychological character change story from its starting point as a pure kink thing. I am deliberately attempting to push the style into a new place for me; I'm getting weary of the writing voice I slip into naturally. Lots of Giles/Olivia, and I believe I have treated her as a human being, though the relationship still ends when she takes off scared after "Hush". 22k words, and still a few scenes only blocked out and not fully written. And-- get this-- Giles not only has kinky sex, he cross-references. Using index cards. Not at the same time, though. That's too advanced for this writer to pull off.
Can you pull it off? Give it a shot!