Ask HN: Tips for Building Customer Survey Forms?

I'm planning on going out into the wild this weekend to hunt down some of my future customers and find out how likely it would be that they would sign up for my service. They'll be congregating in parks and other recreation zones, so I'll be bringing bottles of water which I will be offering in exchange for their time filling out a form. Does anyone have tips for how I should approach this project? How about the types or number of questions I should ask? Currently, my plan is to open up (the form) with general domain related questions (games, recreation and sports in this case). I'll follow that up with internet related ones ("Are you on Facebook?", etc.). Then I'll close by trying to get their email address. I just got a copy of Steve Blanks's book in the mail. I plan on cracking that open tonight and studying up. Thanks!