Acting classes or singing lessons? I think you just want to get confidence in having people's attention, through modulating like the other guy said, and being interesting to listen to. But try not to worry about this too much, I feel like it will make you feel insecure if you focus on it for too long.

Another great thing for me is to shift the focus on to the person you're speaking with, even in a group. People love to talk about themselves. Ask them honest, thoughtful questions about what they're talking about. Don't over indulge them, but everyone is equal in this world, and hearing them out on things leads to a healthy discourse.

One final tip and this is important, if they talk about a trip to the Bahamas or whatever and you then feel the urge to bring up your similar trip to the Bahamas, maybe don't. Instead of hearing their point of view, you're making the conversation about you immediately and people don't like that. You can hold that thought and bring it up later in the conversation, organically.