Most people like to talk about themselves, so if you ask someone about their interests, listen and ask more questions in a gentle way ("Gee, that sounds interesting - what do you like best about it? What made you take up . . .? What is it like to . . .? ) they will think you are a fascinating conversationalist.
On a higher plane, I once read that stupid people talk about other people, normal people talk about events and intelligent people talk about ideas.
Take Hilary Clinton, just to name someone in the news. Everyone has opinions about her. If she comes up in the conversation and you talk about her problems with Bill fooling around, that is about "other people" and a low level of conversation. If you talk about her latest speech, that's an event and middle level. If you discuss her vision of the future, or the concept of a lady president, or other female political leaders in the world, that's an idea and a high level of conversation.
If you are in a mixed group, stay away from politics, religion and sex unless it is in a general way. As soon as you make a nasty joke about George Bush or Hilary Clinton it will turn out the person sitting next to you is a stalwart Republican or Democrat.