Unless the context argues otherwise, I avoid just about anything (a) personal, (b) controversial, or (c) likely to be perceived as “intellectual.” I typically look for common ground, even if only in the shared environment, whether social, professional, or more or less random.
For the most part I don’t want to talk to people who happen to be traveling beside me. I’d rather read or doze or think my own thoughts than listen to someone’s banal chatter and try to respond to it. I don’t happen to think that the best use of shared time in all situations is to exercise our faculty of speech.
However, especially when I’m stuck in a social situation, I remind myself that everyone I meet (without exception) knows something I don’t know. I often look to learn something by asking a pertinent question or making a leading remark. Sometimes you can get more by using what little knowledge you have than by frankly admitting ignorance.