Here's an interesting thing. What do you suppose the purpose of a sex scene is, in literature?
Well, unless you are writing erotica, it's there to... develop plot, reveal character, create tension, worldbuild, and entertain. If you are writing erotica, it should do all those things, and be hot, also.
When writing sex scenes, please keep in mind that real people (a) do not have sex the way fictional characters do [which is to say, like people in movies, either Hollywood or porn, or like people in many novels, either literary or genre. And they definitely don't have sex the way people in romance novels do.] and (b) also do not all have sex the same way that the author prefers to.
Interview your friends. Read a couple of textbooks. Hey! Go out and have some sex, and notice how your partners do it. (Please note: the management is not responsible for any damaged relationships or medical fallout from taking this advice, and does recommend following guidelines for safer sex.)
Real people, having sex, do all sorts of things, including fumbling awkwardly, getting on each other's hair, getting interrupted halfway through and having to come back later (whereby the delay can do all sorts of interesting things to one's physiognomy), and, you know, getting into a really good groove and having the time of their lives. Real sex can be lousy, or mediocre, or pretty good, or triggery, or kind of skull-wringing, and it can carry all sorts of associations and backstory. (I tell people that I write sex and fights and conversations all the same way--it's action and reaction, driven by character issues and agendas, all handled in deference to the plot.)
Sex is not effortless. Nor is it necessarily a complete mess every time it happens, unless you're stuck with somebody who can't read signals or carry off teamwork. (Hint: Before you sleep with somebody, get them to help you move a large piece of furniture. This will tell you a great deal about whether you really want to go there or not.)
Also, by the time two people can carry the nookie off as if it were choreographed, it's probably started to get a bit dull. Or they've been watching too many of those movies/reading too many of those books where it's, you know, smooching, oral sex,*** PIV**** (usually in the missionary position.)
People have different sticking points, and different triggers. One guy may freak out totally about oral sex; the next one may draw the line at anybody more than five years older or younger than he is. This character may hate having somebody else's hands in her hair while she's going down; another may live for it. Think about it. Think about what the character's life experience is, who they are, and where their level of squeamishness is.
Also, if you can't write about something without giggling? Get over that. Because the reader will be able to tell you are squicking. (I'm not saying you shouldn't squick; some things are honestly just made of squick. I'm saying if you can't deal with writing about something matter-of-factly, it's not gonna work on the page. Get comfy, or go write about something else.)
Another thing that serves me well: if you have any particular kinks of your own, unless your characters have good reasons to share those kinks, you might want to avoid writing them. There's a couple of reasons for this: (a) if it's really a hardcore kink, you're going to have a hard time making it seem interesting to anybody who doesn't share the selfsame kink--because the kink itself is enough to push your buttons, so setting it up becomes harder, because you're too close to it. and (b) other people's sexual fantasies are mostly opaque and boring. If you don't believe me, so read some naive internet porn or some of Nancy Friday's work on sexual fantasies. Yawntastic. And mostly no sense of narrative.
Of course, if you are writing erotica for yourself, or for a limited market that shares your kink, knock yourself out. Do what makes you happy. If you're writing in service to a larger non-erotic narrative, however, do be aware that not everybody finds the same things sexy you do. If they're into the character's head enough, though, they may find the things the character finds sexy, sexy, at least for the duration of the scene.
As regular readers know, I'm a big proponent of practical experience and experimentation in all things artistic. If you are writing kinks that are not your own, you might want to either try it out, or ask around a little. (We recommend exercising common sense. Autoerotic asphyxiation*, pedophilia, bestiality, and self-mutilation are probably best not experimented with.**)
The thing with writing good sex scenes, as the thing with writing everything else, is this: telling detail, man. Not a chair: this chair. Not a cat: this cat. Not a sex scene, idealized or farcical, but this sex scene, right here, right now, with these two****** characters having this sex.
When you get the off-beat, perfect detail just right, and it makes the scene concrete and real, that's called fabulous reality.
If you have that, you can do no wrong.
*Although I hear you can fake it with corsetry, but please don't engage in any potentially life-threatening behaviors just to find out if breath restriction really does give you better orgasms. That one falls under the ask-a-friend catalogue.
**Me, I've got this one guy with a serious hardcore pain kink. Now, I've got the pain tolerance of an ox, but I don't even get an endorphin rush from a piercing. This is where I resort to expert help, because my physiology does not cooperate.)
***Even mainstream Hollywood has discovered cunnilingus in the last ten years. I think it's still a bit edgy, though. Shocking!
****penis-in-vagina, a handy TLA***** for when you need to talk about that societally approved form of sex that even former President Clinton presumably considers, you know, sex.
******or one, or three, or seventy
Mmm. Kool-aid. Yes, another author drinking it. (via anghara)
Is there something about too many NYT best-sellers that causes spongiform encephalopathy?