"Show, Don't Tell": the most common error in amateur fiction. · 5:30pm Dec 29th, 2014
I recently left a suggestion on Tala Tearjerker's first posted story. While there is quite the hullabaloo over her deleting comments (not a controversy I fully understand, to be honest), I have no doubt my comment will remain up. Nonetheless, I feel other new authors could benefit from my verbose suggestion, so I've included it below. 
I think the mane (main) thing you need to work on is the number one problem most amateur fiction suffers from. This problem is usually referred to as "show, don't tell" (i.e. that's what you should be doing). This issue occurs frequently in your story, but here is one prime example:
"Surely Tala would turn heads. Rarity would most definitely have approved."
Lines like these force-feed your readers a value judgment. This is almost never a good thing in fiction. What you should be doing instead is this: write the description well enough to allow the reader to come to the desired judgment on their own. In this case, you should be describing the dress without expressing any of the intent behind its design, and without labeling it with value judgments. If you describe it properly, readers will think and feel what you want them to think and feel, without being led there by the hoof.
I would even suggest avoiding comments like, "the dress was provocative for day wear", when possible. While much less obtrusive, this is still a judgment the reader could come to without you making it explicit. Something like that might be necessary if you were describing the social context itself (e.g., if the reader didn't know what was considered acceptable or unacceptable day wear in anthro-Equestria), but in this case it appears that Equestria's standards (initially) are similar to Western standards so the judgment isn't necessary.
I'm being very serious when I say all this. 
"Show, don't tell" is one of the hardest things to train yourself to do in fiction writing, but it's probably the most important. Don't tell me somepony is powerful; show me. Don't tell me something is disgusting; show me. Don't tell me somepony is sexy; show me.
Unfortunately, this is hardest to do when you're writing in third-person omniscient voice, which is a common voice to use. I know you're using third-person omniscient in this story because you describe the motivations behind multiple ponies' actions. In my Twilight's Journal story, I'm using first-person unreliable character voice. That work is not a good example to draw from if you're writing third-person omniscient, because the narrative style I am using allows me to cheat extensively. 
However, the only judgments I can put in my story are Twilight's, which are unreliable. I chose that voice because the entire theme of the story revolves around Twilight's perceptions and how they transform as she herself changes. But even there, I try to avoid adding her judgments when describing a scene (or at the very least, I include a neutral description along with her judgment calls, so the reader can compare the two in a more objective manner). See the chapter where I describe Rarity's dresses for an example of how I balance the two.
If you try to tell the reader judgments in any kind of third-person voice, those judgments don't come from a specific character. They come from you, the author, and that's how readers will perceive them. This makes the judgments feel "forced" upon the reader by the author, which makes it much harder for a reader to forget they're reading a story. Besides, it's really not interesting when you're told what to feel (er, mental fetishes aside). 
Fiction is neat because you can (and should) leave much of the interpretation up to the reader. Sometimes you should even do it with descriptions of things and characters. (For the extreme example, some very famous authors actually never describe their characters beyond, say, "the old woman"; but that's way too far if you want to write an erotic work, heh.) 
Most of the other things I could say are super-duper minor in comparison to "show, don't tell". I strongly suggest focusing on that as much as possible in your writing. I also recommend browsing through the writing guide (it's a drop-down from the FAQ) as it contains a lot of useful information that could benefit your future work.
Feel free to come to me if you have any questions or need other advice.
Don't tell the audience what to think.
Don't tell the audience how to feel.
Don't tell the audience something that they already know.
Don't tell the audience the plot.
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(I don't care for them, but at least you can tell). I mean, if a writer who knows how to write fiction well tries to imitate a terrible author, most of the time they screw it up. Spiderses is a, um, "good" example where it's clear the author is sandbagging the audience. The Eye of Argon, on the other hoof, is clearly legitimate. 
Amusingly, I find adherence to this rule is actually an easy way to detect most trollfics
Even with the quotes, it feels wrong to have Spiderses in the same sentence as "good"...
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...and just for those who haven't heard of Spiderses, here's all you need to know.
img2.wikia.nocookie.net/__cb20111220063930/mlpfanart/images/5/5c/Spiderses_by_yu_jie-d475ndh.jpg
So hawt.
But to be fair, my favorite quote is easily: "Why is everything bigger and eight?"
Absolutely right! Agreed on all accounts.
Telling your audience how they are to feel about something doesn't just damage the illusion, it can (and will!) often even breed resentment. Outside of people with a certain fetish, nobody wants to be told what to think or how to feel. At best, it comes across as lack of talent or effort to let the desired effect build naturally, as condescending and talking down to your audience at worst.
The same thing happens in RPs at times, and it's always highly annoying. I hate it when other players tell me what my character supposedly thinks now. When I'm running a game, I never tell my players "you are afraid" unless they were hit with a fear spell or something, i.e. the crudest form of mental manipulation. Because that's what it is; so is describing a scene or action to elicit a certain emotional response, the difference lies in whether or not you are willing to allow your readers to come to the conclusions themselves—and take the risk that they possibly don't.
I have a problem with the show don't tell maxim for written work. I am almost completely incapable of turning words into visuals. To know what something looks like in anything but the most basic sense I need an image of something
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that's interesting. Generally I want to see the story the author wants to tell