Conversation is a just a game anyways. In fact, it's very much like a game of tennis. Imagine if you will, that you are playing tennis with your friend. Now imagine that your friend has a case of three tennis balls and you are out on the court. Casually, he lobs up the ball and serves it to you. Now, imagine if you just stood there and watched it go by and then just chuckled nervously. Ok, so your friend would get out another ball and lob it across the net again. Then imagine that, again, you just let it go by. One by one until finally after three balls, your friend no longer has any balls to serve. They are all on your side of the court.
Conversation is exactly like that. Imagine if someone comes up to you and says something to you and you just grunt out the bare minimum of "um hmmm" or "fine". You are essentially letting that ball fly past you and eventually, after so many tries your friend will be out of "balls" or intros to conversation. The key is to see the ball coming and be prepared to return it and volley it back and forth. I mean, eventually the ball will get by one of you, but then you have a couple of other balls (or topics) in reserve that can fill out a nice conversation before you run dry.
Let me give you an example of "holding the ball" and letting a conversation die:
Her: Hey, how are you today?
You: Fine.
Her: Uh, did you watch the game last night?
You: Yes.
Her: I was so psyched about how that one guy hit that triple.
You: *nervous laugh* Yeah, me too
Her: *awkwardly* Well, I better go.
You: Ok
Do you see how "You" held the ball? Now, let me give you an example of how to "return her serve":
Her: Hey, how are you today?
You: I'm pretty good. How are you?
Her: Ok I guess. Did you watch the game last night?
You: Yeah, it was awesome. Did you see the game-wining triple?
Her: Yes! I was so psyched about that.
You: Yeah, me too. Derek Jeter is awesome. I met him one time.
Her: You did? You are soooo lucky!
You: etc. etc. etc.
Do you see how much smoother and easier that played out? You led the conversation and captivated her interest. And you didn't have to say anything monumental. You just had to say the first thing that popped into your head (that is appropriate for the level of friendship of course).