bro, imo one should always think before sayin...unfortunately, too many of us just blah out whatever comes to mind and then regret it
normally, people talk more than they should - the key thing is packed in 4-5 sentances, and the other 30 sentances is normally unnessesary "verbal decoration"....naturally you will be able to pick up those key things easily...but don't interrupt - while they are busy w/ their "decorative" sentances, u will have time to shape your responce better... once they stopped, pause for few seconds...by this time you will prolly have an idea of what you want to say..
its not as hard as it may sound, and mostly comes to us subcontiuosly...even if you pause for few secs before saying it is most likely that you'll say it better than if you just said it immediately
of course, this is assuming meaningfull conversation, like business discussion, not a casual chit-chat at a party...
anyways, comminication is an art....ancient greeks used to have schools that tought the art of speech...look at it as a chess game: learn from repetition and strive to improve continuosly
hope this helps