Simply ask them if they're going to. So says Daniel Kahneman, a Nobel Prize-winning psychologist:

You call and ask people ahead of time, "Will you vote?" That's all. "Do you intend to vote?" That increases voting participation substantially, and you can measure it. It's a completely trivial manipulation, but saying 'Yes' to a stranger, "I will vote"...

According to Kahneman, making this sort of commitment -- even to someone they don't know -- can help motivate people to get to the polls on Election Day.

So... are you going to vote?

(via Marginal Revolution)