This is where those crazy ideas become a bit more refined. You begin to weed through all your ideas, deciding which ones are feasible, which ones are not appropriate for your intended audiences, and so on. Start with pen and paper and draw out your game. You don't need to be an artist; prototyping is rough, it's messy, it is completely raw. Don't get caught up in how neat it looks. The point at this stage is to get what's in your head out on paper. Other things that you might find useful during the prototyping stage are post-it notes, colored pens, scissors, dice, counters (for example, beads, buttons, stones, and so on), other game bits and pieces (for example, Monopoly money, figurines, and so on). During the prototyping stage, you will want to also see how the interaction flows through the game. For example, does the interaction feel difficult in the sense you can't do or get something that you want to? Perhaps the game feels a bit too easy or hard? At this stage, these are considerations that you will also need to iron out when it comes to properly playtesting your game, so don't worry too much if they still don't feel completely right.