For heaven's sake, folks! Don't write about things you don't understand, and don't use other writers for reference, especially when writing about sex. They may not know any more about it than you do. Here are some glaring examples of mistakes that people who write erotica often make.
Squirting sperm into a partner's womb; fucking her womb or cervix:
Uh...you can't do that. The cervix (the lower third of the womb, or uterus) is effectively closed until a woman begins labor. It opens slightly during menstruation, but the opening is still far smaller than a penis and can't be penetrated by anything approaching that size. Under any conditions, sperm can make it; a dick can't. You can't fuck her cervix, either. Besides being too big to enter, a cock isn't that stiff. It would bend, and you wouldn't like that at all.
Ripping off panties in shreds, or removing them in other non-standard ways:
That can possibly be done, depending on the panties, but while you might like the results, your partner definitely wouldn't. That material is strong! Bruises and probably lacerations are guaranteed, unless the garment is incredibly flimsy. My ex-wife and I tried it once with a flimsy pair of bikini panties. They didn't tear, the waistband didn't break, and she got ugly red contusions that lasted for two weeks.
Butt fucking:
Entry: There are two sphincters in the anus, the external and the internal. The external can be relaxed voluntarily - with practice. The internal sphincter is involuntary and must be stretched slowly, otherwise there is intense pain. Popping the head in and burying your tool to the hilt is pretty-much guaranteed to cool off the fuckee and make subsequent opportunities less likely.
If you don't believe that, find a policeman's nightstick, grease it up good, and quickly shove about five inches up your ass. Unless you have a lot of butt-stretching experience, you'll only do it once.
Violent, prolonged ass-fucking: The membranes in the anus and rectum are quite delicate. They need a lot of lubrication. Rapid, extended intercourse is likely to injure the membranes and can lead to some pretty severe problems, including hemorrhoids. Doing it often will likely lead to a search for a different butt to fuck.
Excesses in descriptions: Unless you're entering the "Dark and Stormy Night" competition, where participants compete at creating corny prose, avoid things like this.
"I blasted a gallon of jizz into her sperm-starved pussy. My incredibly horny girlfriend bucked her slim, sexy pelvis beneath me, thrusting her amazingly firm tits against my naked chest while she screamed her ecstatic bliss. Every muscle tensed as I grasped her body with savage power, pounding my pelvic bone against her crotch as my diluvial torrent of baby batter poured forth. Together we scaled the peak of total sexual delight."
Are you fucking kidding me?
If you wouldn't use language like that while talking, don't use it when you write unless you're creating bad poetry. Complicated descriptions are hard to read. They make your sentences clumsy and break up the flow of the readers' thoughts. Piling on more words is no substitute for well-crafted imagery.
Clarity is always better than trying to be clever. The best writers strive for clarity in as few words as possible. Read some Hemingway. In fact, read a lot of Hemingway. It will improve your writing.
Eschew Bulwer-Lytton. (See, I can construct a fancy, obscure sentence in only three words. That doesn't make it a good idea.)
Generally speaking, use one or, at the most, two modifiers (adjectives, adverbs, etc.) with any noun.
NO: stunningly gorgeous, busty blonde bombshell; stunningly gorgeous blonde babe of a sex toy, and similar indulgences.
YES: stunning blonde, blonde bombshell, busty blonde. Gorgeous, busty blonde -- if you must, on rare occasions -- or just lose the modifiers entirely and settle for blonde or bombshell. Girlfriend, lover, my sweetie an similar expressions work well, too.
Keep in mind that if you've described the person already, repeated descriptions - especially if you're repeating the same phrases - will soon bore your readers. They are marks of a writer who covers up lack of imagination with uninspired gobbledygook.
Careful proofreading is good, too. If you can't find a competent editor and can't do it yourself, use a program like Grammarly or one of the other correction aids. If your editor is competent, they will suggest quite a few corrections. If they don't, get a different editor. Nobody's perfect.
The tendency for online writers to use voice recognition software turns out many words quickly, but does not encourage good editing. If you use it, be especially careful about proofing and editing your work.
Many of you will reply that you write for yourself, and you like it that way. Whatevers. Or, you could try doing better and learning something new.
There will be more of this sort of thing. I'm just as critical about my own writing, so I'm allowed.