The next step is to come up with basic rules. If your problem statement suggests mechanics, this should be easy. If your problem statement suggests theme, then you may want to consider what mechanics may match that theme. It’s not important that you get the rules right on your first try, because everything is on the table as far as change goes. In fact, the first version of 7 Wonders was not about card drafting at all.
Write these rules down on paper or in a digital document, but go only so far as to make a playable game. Do not worry much about the edge cases or complicated matters—the key is to have enough rules to make a playable game. The goal is to build your first prototype.
This prototype is likely to have breakable systems, unnecessary materials, ambiguities, and imbalances. You will have plenty of time to iron these out through playtesting and revision. The key of the first prototype is to get a feel for the game.
The first time that you play your new game, you are quite likely to identify many areas in which the game needs to improve. Perhaps there are not enough interesting decisions for players. Perhaps the rules are unclear about edge conditions. Perhaps the game always plays out in one particular way. Perhaps real players do not do what you expect. These are all areas I’ll cover in upcoming sections and chapters, but to apply any of these lessons to your game, you must first have a game on which to test them.