I cannot stress attention enough, particularly with all of us and our smart phones receiving blings and blangs from every which way, telling us about a birthday, a successful souffle, a poopy diaper. And I'm so terribly guilty of checking my phone, of looking at the tv screen behind the person's head, of checking out the patrons walking in and out of a restaurant, instead of focusing on the person talking and what he/she is saying. On top of being easily distracted. You won't have a good conversation if you miss every other word a person says. Or if you forget what the point they made five minutes ago because you weren't paying attention. That being said, if you're looking to end a conversation quickly, do all those things above, simultaneously.
Interest / openness is where I suppose the subject of the conversation comes into play. If you are not interested in the topic at hand or even open to the topic becoming the focus of the conversation, poof the conversation is lost, at least on that point. What does Penny tell Sheldon in TBBT - improv is all about saying yes. It applies to conversations too, which doesn't necessarily mean agreement on the topic but agreement that it should be one that is discussed. Some of the best conversations that I've had have been about the most obscure of subjects but it's the willingness of the parties to explore the topic and its different angles that made it memorable.
And the last one is an obvious one but interaction is key. I am certain that we have all been part of those one-sided conversations, which by the way is called a monologue, where you could put the phone on mute, come back in five minutes, and not miss a thing. Or sit nodding yes like a dashboard bobble head for half an hour. Remember kindergarten playground rules. Take turns. Try not to interrupt (guilty of this as well). Also, ask questions. Because sometimes the answers may surprise you. And in a good way.
What is the last really good conversation you had and what did you talk about?