depends on what type of game. you can always run ads or if its a point based game you can try a content locker and give points for that
Idea of running ads i like better. Maybe you know some good advertising networks that allow game and app developers use ads to make money with facebook games and apps?
I also like the idea of runnin ads for the games, since FaceBook ads are tareted. Some ideas of games that you can create are: 1. A virtual reality game that requires you to spend money to purchas different things, such as property. 2. A game that requires points for different functions, and the points have to be purchased. You can allow so many points to be purchased for $1. 3. A game that requires purchase in order to play. I hope that these ideas help. May you have great success.