Good player materials elevate good games into being great games, and can drag great games into being just good games. But they do not fit neatly into the confines of the theory and method I propose.
The player materials are the bridge between Play and System for most players. It’s the thing that guides their actions unwittingly, by providing them with things they can do, should do and shouldn’t do. Their importance cannot be understated. They are the key to playing the game for most of the players, and thus it has supreme importance in according to controlling your Gameplay. Having too much stuff on your character sheet is intimidating, and having too little or missing key aspects just makes the game feel unfinished.
Actually making player materials
Important thing is to think about them from the perspective of the one who writes on it. Make the player materials include everything a player needs to know about most of the spheres of gameplay. Some spheres like character creation and advancement can be handled outside of it, but the most important spheres during play should be entirely playable without needing to reference the rulebook or writing additional notes. If you ever see a player scribble information on the character sheet, you might have neglected some aspect of your player materials.
In physical terms, have a clear separation of features, so if your combat features require an entire page, make them an entire page. Think about the player’s perspective here. They want everything they need at a given moment to be accessible to them without searching for it. If that is impossible, your game might be bloated with features.
Never require your players to memorize too much stuff at once. Provide them with shortcuts that help them remember the necessary things, and if needed, just list out necessary things from the book into the player materials. Don’t think of the player materials simply as somewhere to track your character’s features and so forth, use it as a way to implement the kind of gameplay you want.
Want fast gameplay? Implement shortcuts for common things the characters do, like “common actions” and their mechanics.