Writing smut, like any other kind of writing, takes a certain amount of skill and knowledge. Some writing skills are not required, such as establishing characters or plot development, because the only thing the dedicated readers of smut care about is graphic sex, and the more detailed it is, the better. Character is less important than the sizes of his cock and her tits. The plots consist of: A and B get together. They have sex. They have sex again, probably in a different way. They have sex another time, probably a third different way. Besides A and B, you can have C and D and E or any number of people, and they can have any number of sex acts, performed any number of times, depending on the length of the story.
I hope you notice I made no reference to fucking. Although it is an important part of smut, not every tale has to include fucking. Two men can take turns sucking each other off, or a man can eat a pussy for the entire length of the story, or a woman can do the eating. You might want to write about a man wanking or a woman frigging or two people masturbating each other or a whole string of people using dildos on each other or giving each other hand jobs of one kind or another. This is an area that involves individual preferences. Personally, I like writing about a variety of activities.
However, this is not as easy as it might sound. You could write: Mary sucked off Johnny. Johnny ate Mary's pussy. Johnny and Mary fucked. This would be a form of smut, of course, but of such abysmal quality that I'm sure that Literotica wouldn't even accept it, even if it happened to be 750 words long. I know I would never submit it but I might use it as a story outline. If I did, I would add details and dialogue until it was a 5,000 word story of the hot sex that Johnny and Mary had together. I will, hopefully be describing here how to convert those three sentences, or three similar sentences, into a 5,000 word story that will make people wet or hard, depending on gender.
As in any kind of writing, mechanical skills are important. For one thing, you have to spell correctly, and that requires more than Spellchecker. You can catch some misspellings and typos with the program but not all. If you type in something that is a word, but not the word you want, Spellchecker will not catch it. A smutty story does not have to read like an essay written by a professor of English but, as in any story, the writer should follow the rules of ordinary good grammar. Your computer will not catch all grammatical mistakes so careful editing for them and for spelling errors is necessary.
Also in common with any kind of writing, word selection is important. Avoid repeating names or words too often, especially long words. You can't completely avoid the repetition of articles and some pronouns but keep it to a minimum. Especially avoid starting a string of sentences with the same pronoun, such as: "He unbuttoned...He removed...He looked...He caressed...He licked..." Use proper names some of those times, or other references, such as "the young man" or "the blonde" or similar designations. Sometimes it might be better to combine two short sentences into a compound one or start some of them with prepositional phrases. One way to avoid using a proper name too often is letting the character have two names, such as Jen and Jennifer, and alternate using them.
Remember, you are writing smut, not a technical paper. Try to stay away from scientific terms such as penis, vulva, vagina, etc. Also avoid being cute with expressions like "honey-bucket" or "trouser snake" or old-fashioned terms like "spend" or "cunny" unless you are writing a story set in Victorian times. Although there are plenty of synonyms, I prefer to use what I consider the most affectionate words, "pussy" and "cock". This is also a matter of individual writers' preferences.
In writing smut, you don't absolutely have to have any dialogue, but it does read better if you do. You can say: "Mary enjoyed the feel of Johnny's cock driving in and out of her pussy." Or you can say: "Oh, God, that feels good!' Mary cried out as Johnny's cock drove in and out of her pussy." That's really two ways of saying the same thing but the second example is better for describing Mary's enjoyment. An important thing to remember is the characters are very involved with what they are doing. Any conversation will involve those activities, and they will talk the way actual people talk. In particular, this means using contractions and sentence fragments and otherwise not always using perfect grammar.
Have them talk dirty. This can be something of a turn-on for the readers and it reflects the way people actually talk in those circumstances. I can't imagine Mary or any other woman saying "Your penis feels very good in my vagina." More likely she will say "I love your cock in my pussy." Or "cunt", depending on how crude you want her to be. However crude or refined a character is, be consistent. Nobody is going to speak of her "cunt" and "tits" and refer to the man's "penis" or "organ".
Adults are not usually going to speak of a "thingy" or a "poo-hole" or use any other childish terms. An exception would be if at least one is roll-playing a child. Then they would use such terms to stay in character. Likewise, you could have a character refer prissily to a penis or vagina but, once they really get into the sex, talk about a cock or pussy. As long as you are consistent with the inconsistency, it's alright, and helps develop the character, making the story more believable. You don't need much character development but it can't do any harm.
Avoid too many short sentences. You should also avoid using sentences that are too long, and include too many clauses or too many prepositional phrases, because such sentences are sometimes hard to follow; the readers are liable to get lost reading them and they might give up and go on to something else, and it is quite possible they will avoid your work in the future, and maybe advise their friends and everybody else to do the same thing. Since you don't want this to happen, avoid sentences like that last one. Personally, at least in the narrative, I try to mix short sentences with longer ones. To me, the story seems to flow better when I combine sentences like that.
You don't need a lot of description of the characters, but you do need some. For readers to relate, they need to be able to picture the people involved in the story. The length and color of the woman's hair is usually enough, but sometimes curls or braids or other hair style might be mentioned if it somehow figures in the story. Information on the man's hair is not usually worth mentioning, although in some instances it might be. If eye color is relevant, mention it, otherwise describing a face as pretty or handsome or other general term is enough. An unusual facial feature, such as a big nose or ears might be mentioned, but only if it advances the story.
All the women in smutty stories have big, firm breasts. Besides being big, they are sumptuous or luscious or succulent or bouncy or similar adjectives, and have big, sensitive nipples that become erect when licked or fondled. Don't mention the exact size unless it has otherwise been made public, such as the woman having been in a beauty contest. Their actual size is of no importance anyhow, just as long as they are big. Besides having big breasts, they are generally sexy, although not spectacularly so. If you happen to be writing about a big, beautiful woman, make sure you emphasize the beauty of her face and how sexy the bigness makes her. Even though some people actually prefer the type, women in smutty stories should never have figures like Ally McBeal.
