There is a marvelous ambiguity in the question that Mike and I are debating. Idiomatically, a question that begins “How do you . . . ” might be asking how one should do something; or it might be asking how, typically, it is done. As with any ambiguity, the interpretation depends upon the context.
For example, if an older person who looks a bit baffled asks, “How do you use an iPhone?,” you would show him how to enter a code to unlock it, how to swipe a finger across the screen to make various icons appear and disappear, perhaps even how to dial a call. If, by contrast, a 20-something carrying an iPad asks “How do you use an iPhone?” you would assume he or she was taking a survey, and you might answer by mentioning your favorite apps and showing him or her some favorite photos or videos.
So, if someone asks our question, “How do you choose when you vote?,” one would consider the questioner. If a neighbor or a stranger asks, one might answer “Democrat” or “Republican,” or “pro-life” or “pro-choice,” or even say “None of your business!” But if a student asks, or someone young enough not to be fixed in his or her opinions and habits, then perhaps the questioner means, how should one think about voting, how should one go about making a political choice?