Let's face one fact in the life of an erotic writer: you have to write about the physical act of sex. A little refresher in anatomy can be of great help.
Not long ago I read a story in which the character had one hand on her clit, another hand at her ass and was using a paddle on the submissive. Now, unless we have had a mutation in anatomy, we have a wonderful piece of alien suduction.
Less dramatic but no no less physically challenging was the scene in which the lover mounted his lady love from behind while, at the same time, kissed her full on the lips. Either he was incredibly limber or she was experiencing a moment of demonic possession and her head was spinning on her spine.
As writers we need to be aware of the physical abilities and limitations of our characters to be able to write a believable scene. I know that some writers become so involved in the scene they are writing the forget the little transitions like turning around, turning over, etc.
Writing about sex is often an exercise in fantasy. It is fine that we wish the act would go on for hours. It is OK that we stretch the physical capabilities of our characters. But one thing we really have to watch is taking that fantsy and stretching (both physically and literally) beyond the realm of what is actually possible.
When your reader stops in the flow of the story, especially in the middle of a sex scene, and asks herself "how are they doing that?" you have broken the mood. As a writer, take time to read what you have written, visualize what you have described, and carefully analyze if the possibility is truly there for the characters to really perform the acts you are describing.
© Shadow Jewel, an erotica writer & editor who shares some of her stories at her website, Shadow Jewel, and writes a column at Adult Backwash, called The Castle, where she writes advice for erotica authors.