[quote=Genkai]
I don't know, if dialogue is just used a filler for a post, I'd get annoyed reading it if it had no merit or value to the post. Don't force writing or try to use smoke and mirrors. I try to discourage posters to rely on just doing a back-and-forth between them and a NPC or secondary character. (ex: someone plays as siblings and they tend to post the siblings interacting with each other and no one else) Collabs are different of course but it's easy to tell if a writer is interested and engaged, or nervous and drawing a blank. Some posts don't need to span for miles and miles, each roleplay is different. I don't fret too much, Rare. In time, your reservations won't be so daunting. You just need to jump in and try, don't psych yourself out or compare yourself to someone else.Just write for you and your fellow buddies. A good story will come without pressure or anxiety.
[/quote]

This, this, this.

But, to expand:

From what I've seen, the Advanced Section isn't monitored by moderators, and so the actual guidelines are to justify GMs enforcing their preferences. That is to say, it's really up to the GMs what their standards are. 

GMs vary. Some value post length. Others don't. I certainly don't when I GM. The reason for this is that post length is a hugely arbitrary factor. Theoretically, you could randomly write five paragraphs on how your character feels about different foods in the middle of a fight scene - it won't make your post better. It'll just make it longer, and worse for it. Probably for this reason, I frequently see posts of just one or two paragraphs in the Advanced Section with nobody batting an eyelid. Far more important, in my book, are decent writing ability, where your post introduces new idea and new drive to the story.

Basically, it boils down to common sense. If the GM is explicitly a stickler for post length, perhaps that's not the RP for you. However, you shouldn't let something so arbitrary put you off giving it a go, especially if you're otherwise confident in your RPing. Give it a go.