The biggest thing I've learned in this regard are a few things:
1. Be positive / optimistic (read Seligman's stuff on learned optimism)
2. Be playful with people (aka not too serious, see creative interpretations in things, roleplay. Doing improv workshops helps a lot)
3. When starting to talk to people, you can:
A. Comment on the situation "This train is going so slow"
B. Give them a compliment "Excuse me, (they look up at you now you have their attention) I just wanted to mention that I like your whole vibe. The guitar, the clothing style reminds me a bit of a hippie actually, haha (they nod in agreement). Yea, just wanted to say it's cool is all."
In most cases the conversations don't go anywhere for me. That's fine. I'm just there to chill and have fun, no need to prolong what can't be prolonged. In one out of 10 cases it goes somewhere interesting.
A related comment I made in a different topic: https://news.ycombinator.com/item?id=34653505