Little of Column A, little of Column B.
It's funny, because I'm an introvert and I've always considered myself pretty shy, but I've had some great experiences chatting with strangers on solo trips. I tend to keep to myself and stay in my own head most of the time, but I have become more and more open to striking up conversation when the moment is right. Sometimes someone else will start it; sometimes I'll catch someone's eye and it'll just seem appropriate to make a joke or comment on what's around us, and away we go from there. Kids are a mixed bag; sometimes they're conversation starters and sometimes parents just want you to stay the heck away--I just limit myself to going, "Oh, well hello there!" if a small kid gets in my space in line (as they tend to do) and either that'll start a conversation with the family or it'll alert the parents that they want to rope their kid in, depending on how the parents feel about it.
The big thing is just reading the room and not pushing if people don't want to talk. If someone seems lost or confused by something I'll try to drop in just a very brief suggestion (or flat out ask if they want help); if they find it helpful and want to know more they'll ask follow-up questions, so there's no need to inundate them with a bunch of info they may not want right at the start. More often than not, once that conversation starts people do want the help, though.
