An RPG corebook is basically a training manual. It says, here is a description of a leisure experience, and if that sounds good let me tell you how to do it.
It’s not only that, of course. Hopefully the text and visuals are inspiring as well; and it’s satisfying to have around as a product.
But you’re transferring information into the reader’s brain. That means you follow some principles.
TTRPG structure principles
Information blocks
Divide the content up into thematic blocks, and use layout tools to make them distinct and easy to process.
Make it easy to find info about a topic for reference. Have a good contents list that works for finding stuff (and perhaps an index in a large, detailed book).
Try not to spread a topic around more than one place, unless it really makes sense to have a more advanced treatment later. (There’s a well-known game on my shelf that’s two books, and you have to flip between the two to understand how combat works.)
Reader-friendly design
Don’t present a wall of text. Do break it up. The headings that you use for structure help to do this, as do boxed text and art. Use fonts and text sizes that are easy to read. If you’re using colour and fancy layouts, make that easy to read too – for instance good contrast between text and background.
Information order
This is a key one. Build up from the basics to the advanced. At each stage the reader should have learned enough to make sense of what you’re saying next.
That can be difficult, as RPG drafts often try to be quite interconnected, with sections referring to each other. Tease out what’s most important to know first.
For instance, I put a short rules basics chapter (often just a two-page spread) before character creation, because readers need to understand what their character choices mean. If they spend character points here, what oomph will it give them? If they have a cool concept, what will help them make that work? And so on.
The balance to this is avoiding overwhelm and distraction. If they have to wade through your detailed grappling rules, they might never get to the fun character possibilities; so confine those to a later section for use once they’re committed. Give out information as needed, but not more than that.
Order of chapters
This sometimes comes up on forums and social media. What order should an RPG’s chapters be in?
The answer is, it depends.
First, see the point above about information order.
Second — what is your game about, what does it focus on, and what (if anything) is innovative or strange? You want to put that up front to get the reader into it (and help them understand the rest of the book).
For instance, if you have a paranormal game set in the modern world, the setting is familiar and you can handwave it in the introduction, but maybe the metaphysics and paranormal entities merit a chapter before jumping into character creation.
If it’s an unusual fantasy or sci-fi world, you’d lead with a chapter about that — maybe not all the detail, but at least an overview. If it’s a game about battling superheroes, maybe you want to head straight into the rules. (But please don’t make a supers game that’s nothing more than gladiatorial combat — it’s been done.)
If there are key aspects of detail, you can make them chapters later on. For instance, this fantasy game has a lot about boats and water travel, so here is a separate chapter with the rules and key things to know (an actual example of organisation that we mutually realised as I was editing a project!).
Editing services
If you’re interested in getting editing help with your project, further info is here and we can have a conversation.