What I want to know: How do you start a conversation with a stranger?
Seriously, my best method of starting a chat with a stranger is making a comment about something in the surrounding environment quickly followed by a question about the other person. Try not to talk about the weather as this usually raises a "red flag", ie I really want to talk to you but dont know how.
After that, it's mostly questions/answers as you start to get acquainted. Question/answer ratio in your speaking time should be around 80/20. Try to keep your answers relatively short, especially in the beggining, so that you don't bore your conversational partner. You can usually tell if he/she is genuinely interested in a subject as he will request more information about it. As for the questions let him/her finish his answer, nod, have an open body posture, copy his/hers with a 5sec delay and while he/she answers think of the next one. Give some time between his answer and the next question (his/hers or yours) but be ready to fire in case the conversation drifts off to that "awkward silence".
In any case try to remember that people like to talk about themselves (hence the question/answer ratio) but this isn't always the case, e.g. you have met an introvert (takes time to start opening up) or someone who's having a bad day (difficult to change his/her mood).
Finally, if you fail, don't sweat it. Find what/where the conversation went wrong change your tactic a bit (alter talking speed, think of better generally applied questions, humor) and try again. And don't forget to smile :)