So...I wrote my first m/f scene the other day, and I think it came out really well. It was harder to do, I think, because I was really worried about messing it up.
One of the things I noticed in writing it...there are a ton of words for male genitalia that are sexy or hot or whatever. There are a million that are gross or degrading, too, don't get me wrong. But there are a lot of ways to say 'penis' without repeating yourself. Cock, member, manhood, hard on, shaft, rod, even dick if used correctly. Boner...not so much. No one wants to read about your main character's raging boner when you call it that. They definitely want to read about your main character's boner, though.
Not so much variety with female parts. Let's start with the top part. Breasts. That's fine. Boobs? That sounds puerile. Tits? Even more so. Mammories? Too technical? Chesticals...you get my drift. Sweater puppies? Gah.
Lower parts are even worse. Using the correct terminology was the easiest. Vagina, vulva, clitoris, labia. Or, what about pussy, cunt, ham wallet, cum dumpster, it just gets worse. Pussy isn't so bad but it seems to imply something dirty, which if you aren't writing a 'dirty' piece, seems a bit harsh.
Better yet, what a lot of erotica writers seem to do is refer to the shape, color and location, insinuating that you are talking about lady parts without saying those clinical terms or using the 'vulgar' ones either. Core, folds, pink intimacy, soft opening, yadda yadda with words that flirt. Maybe I just don't have the vocabulary for it, but I have read a whole lot of smut in my time.
I'm open to suggestions.