Lost Garden: Visualizing the Creative Process
Totally worth reading about how to generate ideas, and turn those ideas into actual games. A lot of people think that game design is Mad Libs-style idea generation. “The game will be a cover-based shooter with a plucky, dwarf hero with microtransaction-based upgrades and cel-shaded graphics.”
The core of game design is more about killing ideas than creating them. The design space is full of possibilities, and you have to identify the possibilities with potential, and rapidly test them, improve them, and cut them away to arrive at only the ideas that will create a great game.