Welcome to [Mister Saint]'s discussion on writing adult material. I probably won't go deeply into prose, and understand that everything I say here is my opinion and to be taken as such. Thoughts are appreciated, just so long as you do not say 'you're wrong, ma'am.'

Let's get started.

[Warning]
Adult material approacheth. Read at your own risk.

What is 'Erotica'?

e·rot·i·ca – noun (used with a singular or plural verb):
literature or art dealing with sexual love.

por·nog·ra·phy – noun:
obscene writings, drawings, photographs, or the like, esp. those having little or no artistic merit.

Thank you, www.dictionary.com for that eye-opener.

The first thing you should think when you read this article is 'who decides what has artistic merit or not'? The answer is, of course, you. It is the responsibility of an artist to understand the depth of the material s/he undertakes before undertaking it. Sex is not a subject to be treated lightly in any regard, writing included.

Part of what makes this writing erotic, obviously, is the theme. Sex. Yes indeed. However, women around the world will tell you that eroticism can exist without sex entering the equation at all. Men around the world will ask you what eroticism is, and if they can have sex with you while you explain. In short, it is my supreme belief that women will always write erotica better than men due to their grasp of what is genuinely sexy outside of the conjugal act itself. It is that category of things that erotica should deal with, primarily. 

How Not To Write Erotica

There are thousands of writers who work with erotic subjects. The bulk of it that I have read (and I have read a share, as it was a fascination for part of my life) simply sucked. Take that as you will. However, the traits that made said writing bland repeated over and over from story to story, and I will list a few of them here. Saying how not to write it is, in fact, vastly easier than saying how to.

* Use of crude, unimaginative language. This does not mean obscene language, which is acceptable at times. This means, for example, "Bob stuck it in Shirley." This tells us nothing, is too blunt, and probably isn't doing anything for Shirley.

* Ignorance of sexual subjects. I read of a writer who'd spoken of the clitoris as at the bottom of the labia. You don't have to take advanced anatomy classes or anything, but if you don't know the specifics of what you're about to write, don't be specific. If you can't define cunnilingus without using slang, you'd better not write specifically about it.

* Unrealistic characters. - Pornography thrives on unrealistic scenarios. Every cable man is hot, every homemaker is sexy and repressed, every woman is bisexual at heart, girls cannot enter a bathtub without masturbating, and they're always willing to shed their clothes and make it without knowing anything about each other, consequence free. Avoid this sort of thing at all costs.

* Use of tired language. - This is a big one, and why I suggest that erotic writing ought to exist primarily in poetic form. In prose, writers are tempted to use the play-by-play method of describing an intimate scene. "I held onto Dylan's wildly flowing mane as he pressed his lips against my bare skin. I..." And so forth. The caveat of this method is that there are only so many words one can use to describe aspects of it. 

I spoke with a writer not long ago about the use of the word 'moan' in reaction to a woman being stimulated. I suggested that it was overused, but as I was suggesting this it occurred to me that there really isn't a dead-on synonym for it. There are some near-matches, but only a few. "Sighed" sometimes works, but evokes the wrong feeling. "Groaned" sometimes works, but is generally used for unpleasantness. In poetry, a writer's cache of expressions is endless - in prose, using language too creatively takes the reader out of the fantasy.

This is not to say that prose erotica is of a lesser quality than poetry. Remember that erotica depicts 'sexual love' and concentrate on everything about sex aside from having it.

Things to Do

Do...
 
  ... write about what you know. We all have fantasies. Flesh them out. It will give your writing more credibility if you write about something you want - and chances are, someone else wants it, too.

  ... write from alternate perspectives. Don't always use first person, or third. Or second! I don't know that there's a fourth, but you see my point. Vary it up.

  ... consider the beautiful things associated with seduction. A hint of perfume, a sparkling eye, a soft touch on the knee or shoulder, whispering, and such.

  ... remind people how it feels to be in love. Or lust, as the case may be; however, keep in mind that at least some genuine affection goes a long way in making erotica believable.

  ... ask for help about subjects you may not know. No one knows all there is to know about sex. Most of us know precious little, in fact.

  ... employ poetic devices cautiously. Yes, use metaphor. Use it in moderation. 

  ... be explicit when you have to.

  ... skirt around the subject most of the time. Hint, don't tell. Leave the bulk of the actual sex to the reader's imagination.

Excercises and Ideas

Here are some things you might try. Now, remember that everyone has a different idea of what is sexy. Yours is the most important in all the world.

1. Make a list of things you find sexy. Clothing, food, even colors. Incorporate a list of nine objects into a piece.

2. Write an erotic piece about yourself. In this poem, you are not the narrator, you are the beloved. However, this poem will still be written in first person perspective. In short, write an erotic poem from the perspective of someone who wants (or is having!) sex with you. Think about what you'd want this person to do, and what you would do to him or her.

3. Write a sexual piece where the most important element is the setting. Do you have a place you would like to be more than anywhere else while making love? Or a place that exhilarates you? 

Summary

Erotic writing is exploring the beauty in sex. As long as you don't cave into the temptation to write about the sticky details in majority, you'll do fine. Remember, erotic poetry inspires amorous and lustful thought. Pornography inspires a trip to the self-service station.