Talk to people who are not like you. A recurring theme on The Big Bang Theory (and with nerds in general, of which I am a card-carrying member) is that Leonard and Co. are perfectly comfortable in their own comfort zones (science fiction, the comic book store, their academic fields) and far less so outside of them. So practice where you can outside of your own comfort zone, whatever that is.
Oh, and the easiest way to carry the conversation is to let the other person do more than half the talking. If you can find a way to ask a person about something they enjoy talking about, just sit back and let them talk a while. Interject with good questions you may come up with as they describe something. Voila, instant social skills and you don't have to do the heavy lifting. Most people love to talk about the things they know (including themselves) and are happy to get more than half the conversation time.
Also, it never hurts to be knowledgeable about a wide array of subjects. My annual subscription to The Economist is money well spent, I am always learning from that publication.