carrying conversation... skills?

Hello everyone,
I seem to have a problem carrying conversations with people. Each time I am in the company in which I am expected to carry a steady conversation I find myself unable to do so.
Each time I meet people everything seem to follow the same pattern of talking about school (I just finished my final high school year and my education is very important for me), talking about few major things that happen in our lives and then the problem comes in.
And it's not that my interests are narrow - I take part in sports and learning latin dancing right now, I consider myself to be quite intelligent as well. In fact, people usually like me when they first meet me.
However, when I try to think of something suitable talk about at the stage when I am getting to know people, something that wouldn't seem as if I am struggling to keep that conversation running I can't really come up with anything. Few people take the lead and everything runs smoothly from there, but most don't and it becomes quite uncomfortable.
As a result, the best relationships I make with people come out of situations where I spend a lot of time working with people or when I spend quite a bit of time with them not having to talk all the time.
Does anyone have ideas on why this happens and how to improve on this?

Thanks!