In all likelihood most authors posting stories to Literotica are seeking connection and approval from readers here—and there's nothing wrong about that. And a good many are also interested in receiving help in developing their writing style and the popularity of their stories. There's nothing about that either. There also are readers willing to help authors develop their story skills and even some able to do so.
That established, Literotica makes feedback giving and taking possible, but Literotica is not a critique site; it's basically a reading site. Literotica makes it possible for authors not to entertain unsolicited feedback. Readers aren't leaned on to provide feedback and authors have no responsibility to accept or respond to feedback. Many writers are posting stories here for the sheer fun of sharing erotic writings with others and have no interest in developing skills. That said, feedback can be very useful in helping a writer to develop her/his skills. The kickers are to discern what feedback is useful and accurate and not to lose one's voice or ownership of the story in the process of adjusting to feedback.
Feedback does aid the author. It helps the author read her/his own work more effectively. It looks at the work from a fresh angle without the preconceived notions behind what the author actually wrote, which may be quite different from what he/she thought was being written and conveyed.
The problem with treating Literotica as a critique site, however, is the anonymous nature—even when account names are used—of gauging what feedback is constructive and useful and what is personal and/or informed opinion of a limited number of writers. Advice is only as valuable as the experience and ability of the one giving advice to be giving advice on that topic. Thus, a reader giving advice needs to be careful to make clear that they are only giving a personal opinion—based on just one perspective out of a huge number or readers on Literotica—or they need to substantiate somehow their ability to give writing advice. This can be established by citing authoritative sources and/or establishing a track record of giving useful advice on the forum or directly as a comment on specific stories.
Giving Feedback on Literotica
Perhaps the first consideration one preparing to give feedback on a Literotica story should cover is what the motivation is for giving the feedback. Are you truly interested in helping the author and are clear that you have the grounding to help the author, or are you giving feedback to show what you know—or think you know—about the issues covered, or worse, to feel superior or to belittle the author?
Remember that it's a reading site, not an announced critique site. You can't assume that the author is seeking help with story writing unless help has been requested (in notes attached to the story or in the forum Story Feedback area). Authors who have contributed stories on Literotica for a free read have a right not to be hassled by vigilante critique, whether or not they have used the "feedback not wanted" mechanisms Literotica offers. Even if you see something in a story that you know is inaccurate or a technical mistake, you should weigh how important this is in the context of the overall story. If you don't receive thanks or you get your hand bitten in either of these instances, you shouldn't be surprised; being willing to be thus accosted was in no way a condition of posting stories on Literotica.
Supposing we've established that you are giving feedback with all good intentions of helping the author develop writing and storytelling skills, above all, remember that the story isn't
your baby
. Your feedback should be based on what the author is trying to do in her/his voice and writing style. Feedback should be careful to preserve the voice and intent of the author. The product of the author's intuition can be queried in terms of what he/she intended, but when suggestions start on how the commenter would do it, the feedback has gone beyond respecting the author's product. Your feedback should be about the author's work, not you. The feedback should truly be interested in the aims of the author in the work or you should be questioning your intent in commenting.
The best feedback highlights issues that pop out as questionable or disturbing the reading or the flow during the reader's experience of the work. Be specific with the points of your critique. Show specifically what you think the technical mistakes are and, if the context breaks down for you, where it breaks down. Don't make detailed suggestions on how to fix contextual breaks, though. Don't advise "Your character should do/say this rather than that." Note what you don't understand and why. Don't take the author out of the judgment seat on what, if anything, to do to adjust the work. Literotica doesn't take the author out of the judgment seat. The author is the last one holding the story file before it is submitted (even if it's edited), and the author is the only one who can make corrections to the story.
Don't go beyond your knowledge base on technical issues. If you question spelling, use a dictionary. If you question grammar and punctuation, use authorities on these. If you aren't sure but you see something questionable, marking a "is this right?" is constructive for the author and not raising the danger that the author was right and you are wrong.
Don't give advice on what is commercial fiction on the basis of having taken high school or college English. These courses teach a different brand of writing. Be aware of how commercial fiction is written before giving advice on it. You can gain experience in this by reading a lot of it with an observant eye and/or experiencing writing it yourself. As an untrained reader, you can still give useful feedback, though, just by noting where the story broke down for you and leaving it to the author to decide what to do with it/whether to do anything (e.g., "In this scene, at this point, when the character does or says this, I stop believing in him. It readers to me as out of character or out of context of the story").
Yes, point out any inconsistencies, discrepancies of fact, or anachronism you find (or think you've found). The most creative way of giving this feedback is not to say, "This is wrong; it should be X." It is to question whether what's written is correct, citing what you think is correct. This is fiction, however, so be prepared to find that the author is using literary license. We all known there are no Burger Kings on Mars (at least yet), but if the author wants to place one there for the story context, that's the author's literary license to take.
Don't expect the author to justify what she/he has written to you. It's not your story, and you should expect no more than a thank you for your help—and not even that if you are giving unsolicited advice (and, no, failure to turn comments and voting off does not constitute soliciting critique). Exit any blow-back argument as quickly and totally as you can. If they don't take your advice, they are the ones who will suffer any negative consequences. If you want to argue a point in feedback, this may say more about your needs than those of the author.