I've been learning how to write for years, and I'm still definitely not there. I have learned a few rules for writing, though. The first is that successful writing emerges from rules. Here are some of the rules I'm following for creating locations for the Compleat Villain project.
I might have things I want to say as an author. This supplement is not the place to say them. Every paragraph should persuade the reader that the location is worth including in their setting. I'm already sold on these ideas. My job is to sell other people, to convey my excitement.
Descriptive paragraphs should fall into one of a few types:
For example, the description of "Sector Zero" in Silverline City should convey clearly what it is: a dungeon crawl for superheroes. It's a black metal cave in the guts of an alien ship, brimming with high-tech goodies and haunted by glitchy war robots.
When I write about Sector Zero, I can talk about a few things: heroes or villains who got some high-tech gimmick from this place; adventures that could happen there, such as "Breaking and Entering", "Clear the Hex", or "Delver's Delight" from S. John Ross's Big List of RPG Plots.
I'm not interested in rehashing the usual Marvel/DC mashup comic settings. That has been done, and very well. I need to produce something that distinguishes itself, without being too alien to interest players.
If I don't have something clear to say about a location, I'll talk out loud as though I'm explaining to someone what I want to say. Then I write down what I said out out.
If I don't have the final polished text for something, I'll write down my best understanding of what it really is, like "dungeon crawl for superheroes" in the example of Sector Zero.
I'll constrain myself on the length of a piece of text. Can I fit the description of something into a single Tweet? Could I explain the concept on a single comic page, using speech bubbles or narrator's captions?
I believe that ideas fill our heads like a queue or a line. We have to pull something out of the queue before the next idea in line can emerge, and it's those later, more polished ideas that I need.
If I'm working on the project, I'll close other windows on my computer. I usually have some music playing, but nothing with noticeable lyrics.
Apps like Hemingway help me keep my text simple. The app will highlight difficult text, and estimate the reading level of your text.
That's it! There's probably more that I do, but these are the important things. Let me know what works for you, I'd love to hear it.