Conversation is a very personal art. Plenty of discussions that some people find enthralling can leave others bored to tears. As with most things in life, there's no pleasing everyone all the time. Instead, the key to being a good conversationalist is pleasing most of the people most of the time. There's still no surefire way to do this, but practicing some general conversational skills can certainly help.
Being a Good Conversationalist
Bring something to the conversation. What interesting things do you spend a lot of time thinking about or doing? These topics can be very convenient because you already know a lot about them, but beware if they are topics that are frequently boring or otherwise alienating to many people. If so, it might be good to think about funny stories you know or general interest topics you have read about recently.
Encourage others to participate. While you have to start somewhere, one of the most common and dire conversational mistakes is monopolizing the conversation. If you notice that you're doing most of the speaking, even if other people seem interested, try to draw them out by leaving more space in the conversation and asking open ended questions.
Follow the topic. If the comments of others move the conversation to a new place, try to go along with it and not go back to discussing the same subject that you were talking about before.
Stay positive. While talking about personal problems is a healthy component of close friendships, it's often inappropriate for casual conversation. Unless problems are something that people seem have in common or seem to really enjoy talking about, try to stick mostly to topics that are interesting or amusing, rather than negative.
Try to be interested. If others seem to be enjoying a topic, try to cultivate a genuine interest in learning more about their perspectives, rather than dismissing them as boring and spacing out. In this way you can stay engaged with the conversation so that it will be easy to participate when a more interesting topic comes around, and besides, you might even learn something.
When all else fails, redirect. If you're really terminally bored with a subject, try to gently nudge it towards something you have more interest in, especially in a small group. A good way to do this without monopolizing the conversation or boring the other participants is to try to ask questions somewhat related to the subject being discussed that interest you slightly more.