We can talk about 120 to 150 words per minute. We think between 600 to 800 words per minute. What these facts mean is that, when you are talking, your listeners are way ahead of you. You can never talk faster than they can think and you are always in danger of losing their interest.
So what do you do to keep hold their attention. You must talk their "language". What this means is that, if you are talking to a group of college undergraduates, you must know their interest, the current trend among them and weave it into your conversation. If you are talking to senior managements than you learn what is that turns their world.
It is impossible to hold the attention of anyone for long periods. Researches done on the human attention span shows that the mind needs a break every 10 minutes. So, if you have to talk, remember to sprinkle your talks with humour or digress a bit every 1o minutes or so.
Also remember that, it is your duty to hold the attention of your listener.