Unless you're a game design prodigy, nobody comes up with the final version of a game on the first try. That's why play testing is so important, but so is making your prototypes efficiently. If you come up with a new mechanic for your game, you need to be able to test it quickly and effectively. I still have a full time job, but when we decided to change the resource gathering mechanic in our prototype of SIEGE! I wanted to test this mechanic as quickly as possible. I made over 100 new cards in under two hours, and here's how.
Things that you should always have on hand when designing a game that uses cards: Card Sleeves, Playing Cards, Index Cards, Scissors, a Sharpie and a Pen. A prototype doesn't need to look pretty, I touched on it in my post about
Playtesting, but to reinforce the concept: prototypes need to be functional, not polished.
Steps I use when prototyping cards:
1. Cut the index cards, don't be too exact, they just need to fit inside the card sleeve
2. Use the sharpie to write the title on each card, this makes it stand out and easy to read
3. Write whatever other information the players need with the pen
4. Slide the index card into the card sleeve
5. Put a playing card behind the index card (I recommend putting it in backwards, so there isn't a phantom number showing through the index card
Doing this is quick, but functional. All of the information the player needs is there and these are easy to shuffle. These cards have a similar feel as a production level card.
Just keep in mind that your handwriting needs to be legible, otherwise that will detract from the gameplay.