>>82108492
Ask about them. Keep it relevant to your surroundings, or what they just told you. If you're at the dog park, ask about their dog. If they mention their family, ask about them. If they mention friends, ask how long they've known each other. If they mention a trip they just took, ask them about that. Look up active listening. Alternatively, look up the Solid Snake Method.
You don't want to interrupt them or talk about yourself at all, because they're probably not active listeners. And you don't want to let them stall the conversation.