Here is a little tip for how you can politely ask people to pose in one of your photographs.
Some people, weird as it may sound, do not like it when you take their picture! That’s why it might be nice to have a little “icebreaker” to introduce yourself, Lomography and why you would want a picture of a stranger.
Awhile back I created some minicards with some of my shots on one side and a short text on the other side. This can be something like: "Thanks for let me take your picture – I think this will become a nice shot! You can find your picture on…
I experienced that people are always happy when they received one of those cards, so it´s more an exchange – I get their picture – they get a minicard!