One confusing thing it usually a long mmm-hmmm sound, especially one that goes down in tone from high to low, indicates that the person is interested and wants you to keep speaking- however, a short, sharp "mmm" that rises in tone can mean "Oh, I just thought of something I'd like to say".<p>Also, consider where in a conversation you are- you should be taking shorter turns when you are just beginning to talk to someone. If a person asks you "How are you doing" or "What have you been up to lately?" you should give them a quick summary and then ask them the same question. This is assuming that it's a social situation where you expect a conversation- don't return the question if your boss asks you what you've been doing, and don't answer at length if the question is just a social nicety. The cashier in the grocery store doesn't want a detailed answer to "How are you today?", you should just say "I'm fine, how are you?"  Hope that makes sense.