Okay, so this might be a bit confusing, but this isn't some quaint piece about daily life - It's another advice you get for free if you're thinking about submitting a story. I'm writing this one as an avid reader of literotica "gay male" stories, not really as an author, but since I am kind of both, I tried to mash up tips and tricks from both angles.
There are only a few things that make a good story unreadable, and they're not something magical or something that you'd need a lot of special talent for to avoid. It actually is pretty easy to make all those little problems besides storyline and creativity go away, and to ignore those things is a sacrilege in my opinion. If you really like your story, you don't go half-assed into submitting it!
Here's the first list, maybe others will follow:
Your character names, their quirks, their background, their looks and everything else you deemed worthy of being written down. If you describe a character as shy, don't make him rush into sex, even if you meant it to be an exception from the norm. Your reader doesn't know your character's normal life, he just knows what you show him - remember "show, don't tell"? This is exactly what those pesky tutors and guides meant.
Also, please try to remember your own character's name. I do know that a new story and a new character take some time to warm up to, and of course to build, but if you do that, take notes. They won't stop your writing spree, and they do help if you pause for a few days and then continue writing. You may not notice the sudden changes, because it probably took you days to weeks to write the story, but your reader will zip through it in a matter of hours, and they WILL notice.
Lost in writing
There are a few different ways to make sure you didn't miss any grammar or spelling mistakes. One of them is the built-in dictionary every word processing software offers. The red lines might be aggravating, but they do actually help to make you notice those little errors everyone makes.
Please also try to keep an eye on punctuation. Remember: punctuation marks aren't herd animals, they like their solitary existence. No matter how many exclamation marks or question marks you put in a row, the sentence won't get any more impact, it'll just look like a teenager's twitter feed.
Hold your horses!
So you finished your piece? Feeling giddy there, pal? I do too, every time I get something finished. I'd love to just slam it into the submission field, fire in some nice labels and yank it online as quickly as possible, because, damn, that one's really good!
Unfortunately that's the road to hell, especially if you just finished writing a second ago. Don't do it!
Having been working on a text for hours and hours on end has made you routine-blinded, which means, even though the mistakes in there are probably very obvious, you simply won't see them. But others will, and to a reader, simple mistakes in even simpler words ("hi"instead of "him", "were" instead of "where", "ho" instead of "who" and so on) look like disinterest in your own work.
As hard as it may be, just put your finished piece aside for at least 2 days, better a week, and then look it over again. You'll be surprised how many mistakes you'll find in there! You may even want to think about getting an editor if you're feeling unsure, but don't forget to at least read it yourself before submitting it!