The first time I made a prototype I started by creating loads and loads of cards. I had a dream about a magnificent 4X game with space battles to dwarf Star Wars, more planets than an astronomers wet dream and a technology tree that would put western culture to shame.
So I created loads and loads of cards. That I designed in Illustrator. One card at a time. And printed out nine to a sheet. And cut out by hand. Once card at a time. And put in card sleeves with a Magic card as a backing. One at at time. (This last one was actually a good idea.)