Hey, there's been a whole rash of this lately (as in, every other story submitted to the forums seems to have the same problem), so I figured I'd make a short thread about it to help authors out or to give reviewers something to link to/copy and paste when they want to talk about this subject. You're free to comment or ask questions about the subject and whatnot. This is just me putting my thoughts down on the subject.
Now, I know it sounds anal, but I just want to say that everybody's eyes and brains process things differently. Moreover, text on a screen is harder to focus on than text on paper. Keeping that in mind, you'll also want to know that in order to get the most responses, you'll need to make things as easy for a passing reader to get through as possible. That means making sure that you accommodate for all of those different eyes and brains.
How do you do this? Two ways.
1. Do not format your text. Little exercise for you. Use color tags to change your text to a dark color. (Purple is particularly good for this experiment, but black works too.) Post and switch your skin to Johto Elite. How easily can you read it without highlighting or copying your work to a word processor? Not as easy as reading a post written in the default color, right? Okay, now change your font size to 1 and write a very long post. Not quite as easily readable as the default font size, right? Sure, you might still be able to make things out, but it takes just a bit more effort than reading things written in the default font. For some people with not-so-great eyes, that means they have to strain in order to get through your work. That's not a good thing.
So, to make things easier for you, don't put font tags on your work. It'll be easier for your readers to see, which means they can focus more on your story than trying to figure out what you're actually trying to say.
2. The bigger problem that I've been seeing a lot is the fact that a lot of people don't hit the enter key as often as they should. As a result, fics tend to be blocks of text with no clear break between every new paragraph.
To make things clearer, there are two times when you need to create new paragraphs: whenever you change topics and whenever a different character speaks. A new topic happens in fiction when you go from describing one action or thing to another. For example, one paragraph might be dedicated to describing a setting, and the next might introduce the main character as he walks down a hallway. For another example, if you're writing about a battle, you might go from describing one Pokémon's move and its effects to describing another.
With dialogue, it seems to be a little-known fact that you need to space things out even here. No, it doesn't make things neater to take out all the spacing between each line of dialogue. You're still starting a new paragraph each time you go from what one character says to what another character says. (Or, in other words, if Character A has stopped speaking, start a new paragraph before Character B starts.)
Now, in print, you'd normally indent (hit the tab key) every time you begin a new paragraph, but unfortunately, you can't indent lines online. (There's an indent tag, but this moves the entire paragraph over, not just the first line.) So, you show a different paragraph just by hitting the enter key twice instead of once.
I know it sounds anal, but it's really important that you remember to do this. Like I said earlier, it's more difficult to focus on text on a screen than text on paper. For some people (like yours truly), it's hard to keep track of what line we're on if we don't have clear paragraph breaks on our screens. It makes us skip lines, reread lines, or generally have our eyes cross. In other words, it's really a pain, to put things bluntly. So, we're less likely to want to sit down and go through your work if we can't get past the formatting because, well, it'd be painful for us. Sometimes even literally if your text goes on for long periods of time.
As a note, yes, I'm aware that some people confuse the word "scene" with "paragraph." Scenes are complete breaks from the action to move to a different location, different time, and sometimes different group of characters. A paragraph, however, is a subset of a scene that captures one topic or character's dialogue. Considering the rules for separating paragraphs, you can't really just separate scenes with a single line of space. There's a variety of different ways to indicate scene breaks, so I encourage you to think creatively about how to do that. However, just keep in mind that a paragraph is (usually) much, much smaller than a scene and that whenever someone tells you to separate your paragraphs, they're not talking about all the action in one location at one particular time.
You may be wondering why I'm telling you all this. After all, the reader has the ability to change their skin or copy your work to a word processor, right? Well, that's the catch. You don't want them to do that because it distracts them from your story. Instead, you want them to be able to jump right in for each new chapter, and you can do that by removing as many obstacles between them and your work as possible. In other words, the easier it is for a reader to look at your work, the more likely they'll be able to sit down and enjoy what's going on, which means the more likely they'll be coming back.
Hope this helps a little!