Hey fellas,
I have some experience in this area, so I thought I'd chime in. While publishing the Scrollworks zine I learned that there are two types of writers: story guys and rules guys. Sadly, it's hard to find a person that can do both jobs equally well.
The story guy can write screaming good modules and NPCs, but he's sloppy or not so good with the rules. While writing a stat block he forgets that humans get an extra feat to start with. The rules guy can write a flawless stat block, but his NPCs and modules read like stereo instructions.
On a project, it's best to have three guys: 1) Story guy who writes the module or NPCs, 2) Rules monkey who lives and dies to calculate attack routines, and 3) an editor to check story guy's grammar.
I found that Scrollworks articles that had three folks working on it were rules tight, read well, and had few errors.
That, and you really need a proofer (NOT one of the three above) to go through everything once the project has been formatted and printed. It's amazing how many mistakes happen during layout.
Finally, it's important to have lots of time for the project. The highway and publishing share one thing in common: Speed kills.
When you find errors in RPG projects, chances are one person was wearing more than one hat. i.e. Writing the scenario and doing the rules stuff.
Speaking of errors, any errors in this post are blamed on a fine product from Sweden - Absolut vodka. I love them Swedes.
Oh, visit my webpage and pick up iron rations. It's the shiznit, my nizzo.
PS: You sometimes come across people like Mike Mearls who hawg all the talent and can handle all aspects of the game design process. Bastidge.