I've been struggling with the amount of time my kids are engaged in games on computers. It has gotten to the point that we just put the tablets away and lock down the computers so they don't have any time on them. But they are just as hooked on reading, too! Nothing gets done and I'm really tired of nagging for homework and cleanliness. I wanted to find a compromise that would encourage them to get things done that need to be done first, and then use game time sparingly.
I made these 2.5" x 3.5" cards that grant the child 10 minutes of device playtime for being awesome. A list of awesomeness is on the reverse of the card, to encourage them to continue, well, being awesome. In the beginning, they each received a playing card that explained the simple rules of the game.
So far, it's working without too many hiccups. 10 minutes might be a bit too much, because they've learned how to earn cards quickly, which is exactly what I was expecting.