I've written before about game writing.
Beyond the very basics (have a contract, read the contract, submit what was contracted on time, have an editor that isn't you edit the work), I have some other tips.
Here are some random things I've learned writing for potential use by others.
- If you're presenting a location, a map is critical . . . if the location operates in any way like a tactical, explorable area. If it's just a "menu town" don't worry about it. In that case, you don't even want a map - a picture would do it better.
- It's hard to include full context, but you never feel like you've given the reader enough. The school of thought of "just some single-line notes" conflicts with a need to provide more. The best example I've seen of short, pithy descriptions is the excellent Stonehell dungeon. But it also has larger chunks of information. Getting that balance can be tough - when can you get away with one line and know the GM has enough to work with, and when do you need to explain more? They're paying for your explanation and for usability. For a wordy guy like me that's a tough line to hew to.
- Exceptional versions of monsters are harder to use in play if they're just a set of modification notes ("Snarky snakemen have +1 to IQ, +1 all weapon skills, and Rapier Wit, while Sneaky Snakemen have +1 DX, Stealth-16, and +2 to all weapon skills and a net +1 to Parry.") However, if you write them up as full templates, they double, triple, or quadruple the space needed in the product you're writing for. That goes for any size of template, in my experience.
- Just because you do it that way, doesn't mean the rules do. You need to cross every t and dot every i. My advice is to look every rule up that you reference. All of them. Read each one fresh before you use it. After a while, you won't need to look them all up and read them . . . but look them up, anyway. This is especially true if the GM might need to look it up - provide a page reference. If you depend on a specific set of rules or rule assumptions for something to work, make sure you include them. And make it clear. GMs who don't use said rules need to know this material won't work as written for them.
- run your material past playtesters who aren't you and your group. They will do things differently, and find they need things that you didn't think needed inclusion because they aren't critical to your playstyle.
I hope that helps others.