A friend of mine once rang me up, slightly moithered, to say that he'd spent the whole morning trying to write a sex scene with out using the word throbbing, and I think he was on to something. Unless hardcore is your thing, less is definitely more. As with the sex act itself, what goes on in your head (and therefore in your readers') is every bit as important as what happens physically, so as with all things to do with creative writing, it's a question of striking a balance between firing the imagination of your reader and doing all the hard work for them.
The inestimable Margaret Atwood once said, "Sex is not just what part of whose body goes where. It's the relationship between the two participants, what gets said before and after, the emotions -- act of love, act of lust, act of hate, act of indifference, act of violence, act of despair, act of manipulation, act of hope. These things have to be a part of it." Anticipation is a key element, and the context of the lovemaking is important, as are all the undercurrents - in the real world, sex can be a vehicle for other emotions and needs, it can be a transaction, it can also be a moment of sublime consummation, and the same is true in fiction.
I'm instinctively reticent about using my own work as an example to show how I would tackle something, but I guess as sex is my subject then I'm likely to be blushing anyway. So, in trepidation, here is ashort excerpt from my current novel, in which nothing actually happens - it's all about what just might...
Have a go yourself. Be oblique; with the erotic, indirection often finds direction out. Use euphemisms if you feel you have to (think DH Lawrence's John Thomas) although try not to be coy. Be heartfelt, or wry, or cynical or romantic as the occasion demands, but enjoy what you are writing - it's difficult to fake it!
She didn't speak. Her smile widened, not flickering this time, and his mouth moved a fraction as if in answer, although he had no idea what he might say. Phrase by phrase, in stealth, a silent dialogue began. They talked of kissing, of the slow stroke of tongue on skin, of clothes sliding, of the serration of a sigh, of the endless raising of an arm, of a head turning blindly; they talked of the thready feel of a sheet, of a hip jutting white, of saliva and sweat mingled and sweet, of the delicate violence of touch.They never drew breath.