If you're in a situation where it's not necessarily common to approach strangers, you'll probably have to to come up with some "excuse" for talking to them, like "that's a cool shirt" or "do you know where the library is?". Then you have to transition that into a conversation somehow. I'm not really sure how to do that part.
Here's a recent example (with a lady sitting beside me in the aeroplane; translated):
from which it was trivially easy to start a conversation.
Well, you did start with introducing yourself, as opposed to a situational "excuse".
Edit: Or actually, she introduced her self.
r/Fitness does a weekly "Moronic Monday", a judgment-free thread where people can ask questions that they would ordinarily feel embarrassed for not knowing the answer to. I thought this seemed like a useful thing to have here - after all, the concepts discussed on LessWrong are probably at least a little harder to grasp than those of weightlifting. Plus, I have a few stupid questions of my own, so it doesn't seem unreasonable that other people might as well.