Step 1: Idea.
Here are some examples:
Subtracting health (Pokemon or Bakugan)
Three strikes your out (Redakai)
Majority (Instructables card game)
Be sure to chose a theme too. I chose a medieval card game with castles and dragons. Then after i chose the theme i chose a title Castle Quest was mine but you can come up with your own. Make sure the title portrays the game too.