I find that the easiest thing for me to talk about with people is animals. More specifically, listening to stories about their pets. It's an easy conversation to start, and an easy one to continue, because people love to talk about their pets, and love having someone who wants to hear about it.
Other than that, I usually try to get a feel for what the other person's passion is, and formulate a conversation around that. Could be philosophy, could be tigers, could be gardening (another easy topic). It helps to have a wide range of interests, lots of curiosity, and bits of knowledge so you can talk about almost anything.
If all else fails, ask them what they do for a living, or where they went to school, or where they are from originally. Ask lots of questions.