Conversation itself is like a unique dance, one person leads and the other follows the steps. The only major difference is that the two different roles of who is the leader and who is the follower, are always changing. thus, conversation itself involves a bit of effort, which itself can be a pleasure, of course, but you must put forth an effort either way so that everyone benefits. A person who is considered a good conversation-maker is above all else a fine listener. You must not be self-involved to the point that no one wants to listen to you. This will destroy any hope of having a meaningful conversation. You should concentrate all of your attention on the person with whom you are speaking.
It's off-putting, to say the very least, when you must speak with someone who is looking about the room and whose eyes are shifting this way and that as people walk by. A story was relayed to me about a person who met Jackie Onassis at a large social gathering. She said that Mrs. Onassis focused in on her as if she was the only one that was in the room. Even thought there were hundreds of people there and lots of conversations being had. Mrs. Onassis knows that if you make the person in front of you feel special and interesting, then it will foster good conversation.
If someone that you're in a conversation with has strong feelings or opinions on a subject that arises, you should not go with the opposing viewpoint just to play devil's advocate. This sort of hostile conversational approach will at best lower the vibe of those present and disturb the natural flow of conversation. At worst it will lead what could have been a decent exchange of views into an all-out argument. Going with an honest response to someone strong viewpoint is the best way to light up a sincere and genuine debate.
All too often we are put into a conversation where we can recognize someone who is not paying attention at all, only waiting for their opportunity during a lull to interject their own comment or anecdote. This sort of attitude does not create a conversation, only a series of disconnected monologues. No communication occurs. To avoid this yourself, be sure to wait until the other party has finished their thought and respond accordingly to what has been said. If you are unfamiliar with the topic under discussion, do not nod your head pretending to know. It's much more effective to just claim ignorance and give positive interest by asking exploratory questions. You will find that most people will be flattered that you're interested and will gladly answer any of your questions.
In today's society it's still rather common to avoid discussions about sex, religion, and politics, you can still feel free to bring them up in conversation. But tread lightly. Get to know your audience first. Listen to what's being talked about and you can decide what is appropriate. Also, be aware of regional peculiarities. What's common in NYC is not necessarily the general rule of thumb in rural Iowa.