You may have already seen this but this is how it's written in Basic Instinct...
*******************
INT. A BEDROOM - NIGHT
It is dark; we don't see clearly.
a man and woman make love on a brass bed. There are
mirrors on the walls and ceiling. On a side table, atop a
small mirror, lines of cocaine. A tape deck PLAYS the
Stones: "Sympathy for the Devil."
Atop him... she straddles his chest... her breasts in his
face. He cups her breasts. She leans down, kisses him...
JOHNNY BOZ is in his late 40's, slim, good-looking. We don't
see the woman's face. She has long blonde hair. The CAMERA
STAYS BEHIND and to the side of them.
She leans close over his face, her tongue in his mouth...
she kisses him... she moves her hands up, holds both of his
arms above his head.
She moves higher atop him... she reaches to the side of the
bed... a white silk scarf is in her hand... her hips above
his face now, moving... slightly, oh-so slightly... his
face strains towards her.
The scarf in her hand... she ties his hands with it...
gently... to the brass bed... his eyes are closed...
tighter... lowering hips into his face... lower... over his
chest... his navel. The SONG plays.
He is inside her... his head arches back... his throat
white.
She arches her back... her hips grind... her breasts are
high...
Her back arches back... back... her head tilts back... she
extends her arms... the right arm comes down suddenly...
the steel flashes... his throat is white...
He bucks, writhes, bucks, convulses...
It flashes up... it flashes down... and up... and down...
and up... and...
**********************************
Works for me. Even without the ice pick stuff. Although this is Joe Eszterhas who could
write pretty much whatever he wanted. I actually think it's pretty restrained for his style.
This is how Jonathan Hensleigh et al do it in 'The Rock'
********************************
EXT. GOODSPEED'S HOUSE - ROOFTOP - NIGHT
Tarpaper and gravel roof. Candles burning. Loretta
Lynnls "Stand by Your Man" on the boom box. AMONGST THE
RUSTY SUPPORT SCAFFOLDS of an old sign from the 120's --
CARLA and GOODSPEED are, to put it delicately, madly
passionately athletically f*cking. Standing up. They both
have robes on. A CORDLESS PHONE RINGS. Again.
********************************
And to balance it out, this is from Meet Joe Black by Bo Goldman.
********************************
She gets up, closes the door, sits back down again next to
Joe. A warm, awkward silence, they move closer to each
other, now they fall into a foreplay which Susan recognizes
as such, Joe, on the other hand, participates hungrily but
has no knowledge where it is leading. His movements are
instinctive, the smell of her hair, the shape of her fin-
gers, odd things about her seem to interest him. This
excites her because she senses his untutoredness and the
very sense of that stirs her, their reactions to each other
are intuitive and spontaneous; even though Joe has no know-
ledge of how to make love to a woman, ironically his actions
are such that they never beg the question -- has he done it
before.
Strange territory for Joe, not to be 'in control' and exert-
ing his power, but his inventions and responses in lovemak-
ing are so real that an emotional exchange between he and
Susan builds. Joe has found himself in an unexplored land
of feeling and passion, he loves what is happening and yet
at the same time, is terrified by it. He feels himself being
lured by some power he has not only never been aware of, but
is deeply dangerous to partake of; he knows what he is doing
is putting who he is at great risk, yet he goes right on.
The powerful contradiction is transmitted to Susan, and in
the end there is the knowledge they have together made a
journey, they both have been swept away in a stream of events
they have created; and they don't care about the consequences.
Spent, they lie in silence. Finally Susan speaks:
********************************
I've only ever written one horizontal mambo scene and I have to say, I took the Meet Joe Black approach, though not to that level of minutiae. I think the most important thing you can do is make sure it's appropriate to the tone of the story and in your case, where the scene actually opens the story, it's really important to get that tone right from the get-go.