You could start by noticing the small things they are doing, if there are reading a book, or tapping their feet to a particular song. You could do a quick google search and start talking to them about it.
You could notice the things they carry like key chains or mobile covers or a Tattoo or a ID card which gives you any piece of information about them, and helps you start a conversation.
Once you start a conversation its more about keeping them involved by talking about anything from sports to politics, and if everything else fails just talk about the weather.